Publication date: November 11, 2026
What the Overdeck divorce teaches Polish advisers of wealthy international families
The divorce of Two Sigma co-founder John Overdeck, fought without a prenuptial agreement over a fortune estimated at around USD 8 billion, shows how quickly a private dispute can become a risk for a business, its partners and its investors. This study uses the case as a starting point to compare the New Jersey prenuptial agreement with the Polish marital property agreement (intercyza) and sets out what Polish law permits, what it prohibits and what should be negotiated when advising wealthy international families.
An article published by The Wall Street Journal on 31 August 2026 under the title A Hedge-Fund Titan’s Divorce Is Putting Wall Street’s Staggering Wealth on Public View describes the high-profile divorce of John Overdeck, co-founder of the Two Sigma fund, and his wife Laura. The couple’s wealth is estimated at around USD 8 billion, and Forbes lists John Overdeck among the 400 richest people in the world[1]. The Overdeck case illustrates well the risks and problems that arise when spouses with substantial and complex assets do not enter into a prenuptial agreement.
A useful comparison is the 2015 divorce of Ken Griffin and Anne Dias, also mentioned in the article. In that case a valid prenuptial agreement considerably simplified the process and both parties ultimately accepted its terms (Anne Dias received USD 22.5 million, a further USD 1 million for each year of marriage and co-ownership of a penthouse in Chicago). In the Overdeck case, the absence of a prenuptial agreement has led to widely diverging expectations as to the division of assets: John Overdeck has offered his wife a settlement of USD 723 million, while Laura claims 35% of her husband’s interest in Two Sigma, which her lawyers value at USD 6.2 billion.
This raises the further problem of valuing John’s actual interest in Two Sigma, which according to his lawyers is worth considerably less, namely USD 4.9 billion. Laura’s attempts to have Two Sigma’s financial data made public have not succeeded, and the public is excluded from the courtroom each time the matter is discussed, which further complicates and delays the proceedings.
The complex structure of the assets, with no prenuptial agreement in place, has also led Laura to bring separate proceedings against lawyers from Seward & Kissel, the firm that handled the couple’s estate planning. She accuses them of conspiring with her husband, as early as 2005, to give him unilateral control over the couple’s trusts and family foundation. The dispute has therefore spread across several sets of proceedings, with higher costs and a timetable extended by many months.
The article mentions a joint bank account into which Overdeck paid hundreds of millions of dollars during the marriage (and from which Laura withdrew USD 75 million on the eve of filing for divorce). The marital assets also include a property in New Jersey of 6,000 square feet (John has offered to sell his share in the property to his wife for USD 6 million).
By far the most valuable item in dispute is the privately held interest in Two Sigma. Laura values it at USD 6.2 billion and claims 35% of it, that is around USD 2.17 billion. John’s lawyers value it at USD 4.9 billion and offer, instead of a share in the interest, a one-off payment of USD 723 million. A further item is the division of the gains attributable to John’s premarital assets and of his earnings and share in Two Sigma’s investment profits during the marriage, which he values at USD 685 million.
The settlement also covers a charitable foundation with assets of USD 900 million and a number of trusts, including a trust intended to secure the future of later generations of the family (a generation-skipping trust). Finally, the divorce touches on corporate rights in Two Sigma: if Laura succeeded, her stake would change the balance of power in the firm’s governance and aggravate the existing tensions between the co-founders, John Overdeck and David Siegel.
The value of bank accounts, listed securities or real estate is easy to verify, so these assets can be divided or bought out at a specific price. An interest in a private hedge fund such as Two Sigma is different: as the article points out, its value rests largely on paper gains and there is no market price for the stake. Valuation depends on a variety of complex methodologies, which in the Overdeck divorce has produced a difference of USD 1.3 billion between the two sides’ estimates. In addition, the lack of transparency of the firm’s financial data makes it impossible to test the competing valuations thoroughly.
The formal position at Two Sigma is as follows: John Overdeck and David Siegel remain the principal owners and co-chairmen. Because of the conflict between them, they changed the firm’s management and control structure, stepping down as co-CEOs in favour of a two-person management committee, which Overdeck himself later joined. This fragile compromise between the founders could be further destabilised if Laura acquired any influence over the firm.
These four notions need to be kept apart. Economic participation means a right to share in the firm’s profits. It does not necessarily carry any right to manage the firm, although it may be used as an argument for obtaining a degree of decision-making power. Conversely, formal title and control may sit with a person other than the one who ultimately receives the economic benefit.
These factors are central to the division of assets in the case. Two Sigma was founded in 2001 and John Overdeck married Laura in 2002, so he acquired his interest before the marriage. New Jersey applies the principle of equitable distribution to property acquired during the marriage (N.J.S.A. 2A:34-23(h) and 2A:34-23.1). In broad terms, wealth attributable to a spouse’s efforts during the marriage is subject to division, whereas premarital property and its passive growth driven by market forces remain the separate property of the spouse concerned. John therefore argues that a substantial part of the fortune derives from passive growth and is not divisible on divorce. How the assets placed in the trusts and in the family foundation should be treated is a separate question, which depends on when and with what funds those structures were financed.
In her separate lawsuit, Laura accuses lawyers from Seward & Kissel of handing John unilateral control over the couple’s trusts and family foundation in the course of estate planning. John denies these allegations. The underlying problem remains, however: once assets are moved into such entities, control over them is no longer obvious and does not necessarily rest with the owner.
Transfers between wealth structures also make it harder to establish the true value of the estate and who actually bears a cost or receives a benefit. Individual structures may carry liabilities, as with the generation-skipping trust that bought an interest in Two Sigma with money borrowed from John. In other situations such liabilities may be hidden or difficult to prove, while having a real effect on the value of the estate.
A divorce at this level of wealth has a real impact on the way a business is run. Laura is claiming 35% of her husband’s interest in Two Sigma, and a stake of that size would undoubtedly unsettle a governance arrangement that is already fragile. Relations between Overdeck and Siegel have been strained for years, to the point that the firm had to disclose the situation to investors as a material risk and change its management structure. If Laura’s claim to a share of the interest were upheld, the current balance of power in the firm could collapse altogether.
Divorce proceedings also force the disclosure of financial data, including sensitive data about the firm. Laura’s lawyers sought to have that data made public, which the court has so far blocked. Laura herself was barred from testifying and from calling witnesses after secretly obtaining her husband’s confidential emails and committing other violations.
From the investors’ perspective, the risks generated by a divorce that seemingly has nothing to do with them, such as a leak of financial data and other confidential information, are considerable. Despite the firm’s assurances that it is not involved in the divorce, a scenario in which some investors withdraw their capital, reducing the value of the whole business, becomes very likely.
It should be borne in mind that there is no single federal law of marital agreements in the United States: the Overdeck case is governed by the law of the State of New Jersey, and the rules on marital agreements differ from state to state. For that reason, and because of numerous significant differences, the American prenuptial agreement should not be equated with the Polish marital property agreement.
Marital agreements in the United States are a matter for state legislatures. In New Jersey, where the Overdeck divorce is pending, premarital agreements are governed by the Uniform Premarital and Pre-Civil Union Agreement Act (N.J.S.A. 37:2-31 to 37:2-41), adopted in that state in 1988 and amended in 2013[2]. In Poland, the marital property agreement is regulated mainly by the Family and Guardianship Code of 1964 (Kodeks rodzinny i opiekuńczy, KRO), supplemented by the Civil Code (Kodeks cywilny, KC) and the Private International Law Act of 2011 (Prawo prywatne międzynarodowe, PPM).
| New Jersey: Uniform Premarital and Pre-Civil Union Agreement Act | Poland: marital property agreement | |
| Permitted scope | Future spouses may regulate a wide range of matters, including mutual property rights and obligations, management of property and its disposition on divorce, death or another event (N.J.S.A. 37:2-34). | A narrower catalogue: extension or limitation of the statutory community of property, separation of property, or separation of property with equalisation of accrued gains (Art. 47 § 1 KRO). |
| Formal requirements | Written form, with a statement of assets annexed (N.J.S.A. 37:2-33). | Notarial deed, on pain of invalidity (Art. 47 § 1 KRO in conjunction with Art. 73 § 2 KC). |
| Full financial disclosure | Where a party did not receive full and fair disclosure of the other party’s earnings, property and financial obligations, that party may seek to have the agreement declared unenforceable (N.J.S.A. 37:2-38). | The KRO imposes no formal duty of mutual disclosure of the spouses’ assets. |
| Independent representation of each spouse | Failure to consult independent legal counsel, without a written waiver of the opportunity to do so, is an independent ground for unenforceability (N.J.S.A. 37:2-38(c)(4)). | No duty to consult an independent legal adviser. |
| Regulating the consequences of a future divorce | Disposition of property on divorce is expressly permitted (N.J.S.A. 37:2-34(c)). | The agreement regulates only the property regime; it does not extend to the division of property on divorce. |
| Spousal support | Spousal support may be modified or eliminated in the agreement (N.J.S.A. 37:2-34). For agreements made before 27 June 2013, the court could refuse enforcement if the agreement was unconscionable at the time enforcement was sought, for example because it would leave a spouse without reasonable means of support. Since the 2013 amendment (P.L. 2013, c. 72), unconscionability is assessed as at the time the agreement was signed. | Maintenance cannot be excluded or modified in a marital property agreement. |
| Treatment of business assets | Given the wide freedom to classify assets, business assets may be designated as not subject to division on divorce. | Depends on the regime chosen. Under community of property, assets acquired from work and other gainful activity form part of the joint property (Art. 31 § 2(1) KRO). Under separation of property, business assets acquired both before and after the agreement belong to the personal property of the spouse concerned (Art. 51 KRO) and are not divided on divorce. |
| Effect against creditors | The agreement governs relations between the spouses and as a rule is not effective against creditors. In the event of a fraudulent transfer, a creditor may seek to have the transaction set aside as against that creditor under the New Jersey Uniform Voidable Transactions Act. | A spouse may rely on the agreement against third parties only if its conclusion and type were known to them (Art. 471 KRO). If the creditor did not know of the agreement, the regime in force before the agreement applies as far as that creditor is concerned. |
| Applicable law and jurisdiction | The Act expressly allows the parties to choose the law governing the construction of the agreement (N.J.S.A. 37:2-34(g)). | Spouses may submit their property relations to the national law of either of them or to the law of the state in which either of them is domiciled or habitually resident; the marital property agreement is then governed by the chosen law (Art. 52(1) and (2) PPM). |
| Effect in other countries | Other countries will apply their own conflict-of-law rules. | In EU Member States participating in Regulation (EU) 2016/1103, the agreement will be assessed under that Regulation, even though Poland does not participate in it. In non-participating Member States and outside the EU, the effect of the agreement depends on the relevant rules of private international law. |
The marital property agreement is regulated in Art. 47 KRO. The provision defines the subject matter of the agreement, namely a choice among the four contractual regimes provided for by statute: extended community of property, limited community of property, separation of property, or separation of property with equalisation of accrued gains. Spouses cannot create a new regime not provided for in the statute. Nor may contractual provisions infringe the fundamental principles of family law, such as the equality of spouses. That would be contrary to the principles of social coexistence, which under Art. 58 §§ 2 and 3 KC renders the agreement invalid in whole or in part[3]. A Polish intercyza cannot exclude or restrict marital rights and duties, nor can it regulate matters concerning children, succession or maintenance.
Marital property regimes in Polish law
| Regime | Source |
| Statutory community of property | Applies by default, without any agreement |
| Extended community of property | Marital property agreement |
| Limited community of property | Marital property agreement |
| Separation of property | Marital property agreement |
| Separation of property with equalisation of accrued gains | Marital property agreement |
The nature of the Polish intercyza must also be seen against the principle of freedom of contract (Art. 3531 KC). Although concluding the agreement is an expression of the spouses’ autonomy, they are not free to shape their property relations entirely as they wish. They must choose one of the statutory regimes and may regulate their property relations only within its framework.
When drafting an intercyza, attention must be paid to mandatory provisions (ius cogens). Failure to observe them, or an attempt to modify them, renders the agreement invalid in whole or in part:
Within the chosen regime, the spouses may add further provisions that are:
Such provisions are permitted as long as they do not create a new property regime and are not contrary to the law.
The marital property agreement must be clearly distinguished from other legal acts of a similar nature:
Recent years have seen growing interest in regulating property relations by way of a marital property agreement, at the same time as the number of marriages has fallen to its lowest level since the Second World War[4].
Marriages and marital property agreements concluded in Poland in 2025
| Number in 2025 | |
| Marriages | 133,000 |
| Marital property agreements | 69,406 |
Source: Rzeczpospolita
The legal basis for the extended community is Art. 47 § 1 KRO, which allows spouses both to extend and to limit the statutory community by a marital property agreement. Under Art. 48 KRO, the provisions on the statutory community apply accordingly to a community established by agreement, except for the matters modified or excluded by the agreement. The modification concerns Arts. 31 § 2, 33 and 34 KRO, whereas Arts. 341-40, 45 and 46 KRO continue to apply unchanged. Where the agreement brings into the community items that under the statutory community would belong to the personal estates, Art. 41 KRO applies, subject to Art. 50 KRO[5].
Art. 49 § 1 KRO lists what cannot be brought into the joint property. Regardless of the spouses’ arrangements, items such as property acquired by a spouse through inheritance, legacy or gift, and non-transferable rights that can be vested in one person only, remain in that spouse’s personal property. Under Art. 49 § 2 KRO, in case of doubt, items serving exclusively the personal needs of one spouse are deemed not to have been brought into the community.
Characteristically for this regime, the items acquired before the wedding that are identified in the agreement enter the joint property, while items acquired after the wedding are treated in accordance with the provisions on the statutory community, subject to the modifications and extensions set out in the agreement. Management of the joint property follows the statutory community rules, that is Arts. 36-40 KRO.
Income from work, business activity or investments typically forms part of the joint property under Art. 31 § 2(1) and (2) KRO: remuneration for work and income from other gainful activity of each spouse, as well as income from the joint property and from each spouse’s personal property. The components of the joint property may be extended further, within the limits of Art. 49 § 1 KRO.
Where the joint property has been extended, creditors may seek satisfaction from it if the obligation was incurred with the consent of the other spouse (Art. 41 § 1 KRO). A creditor may therefore reach an item contributed by the other spouse that would not have formed part of the joint property under the statutory community. If the claim arose before the community was extended, a creditor whose debtor is only one of the spouses may also seek satisfaction from the items that would have belonged to the debtor’s personal property had the community not been extended (Art. 50 KRO).
The regime has clear advantages. It considerably simplifies the management of family wealth, since the split into joint and personal estates often complicates day-to-day family finances. It also makes it possible to even out unequal contributions to the joint property by bringing in personal assets.
Its disadvantages must not be overlooked, particularly when advising a wealthy international couple. Extending the joint property means losing sole control over items that previously formed part of personal property. It may expose a spouse to the other spouse’s debts and the resulting costs. Division of property on divorce also becomes more difficult, which is why this regime should generally be advised against for particularly wealthy couples.
Unlike the other three contractual regimes, the limited community has no dedicated set of provisions. Its legal basis is again Art. 47 § 1 KRO, which allows the spouses to exclude from the joint property items that would enter it under the statutory community, or to confine the joint property to a closed catalogue of items. The provisions on the statutory community again apply accordingly. The agreement may not, however, infringe mandatory provisions, for example by excluding the duty to contribute to the needs of the family (Art. 27 KRO), nor be contrary to statute or to the principles of social coexistence, as this would render the agreement invalid in whole or in part (Art. 58 KC).
Items acquired before the marriage belong to each spouse’s personal property in accordance with Art. 33(1) KRO. Items acquired after the limited community is established enter the joint property as under the statutory community, with the exception of the categories of items specified in the agreement.
The joint property is managed under the statutory community rules, while each spouse independently manages the items excluded from the community as part of his or her personal property. Depending on the spouses’ arrangements, income from work, investments or business activity may be excluded from the joint property and form part of personal property.
An agreement limiting the statutory community is effective against creditors who were aware of it (Art. 471 KRO). If a creditor was not aware of it, the agreement does not operate against that creditor, for whom the spouses remain in the regime in force before its conclusion.
The advantage of this regime is that a potentially risky business activity or investment can be carved out in order to protect the joint property. It carries, however, a risk of economic inequality where highly profitable items are excluded, and a risk of liability for the other spouse’s debts where creditors were unaware of the agreement. The regime may be attractive to couples in which one spouse runs a business and makes investments but still wishes to retain a degree of community with the other.
Separation of property is likewise provided for in Art. 47 § 1 KRO and regulated in more detail in Arts. 51-511 KRO. Under this regime, each spouse retains the property acquired before the agreement and the property acquired later. If the agreement is concluded before the wedding, no joint property arises at all, and each spouse manages his or her property independently (Art. 511 KRO). Beyond establishing the separation itself, the agreement leaves little room for regulating other matters.
Property acquired after the wedding enters the personal property of the spouse who acquired it. An item purchased together does not create a marital community: the spouses become co-owners in fractional shares within the meaning of the Civil Code and are subject to its rules (Arts. 195-221 KC). There is one important exception, in Art. 30 § 1 KRO: spouses are jointly and severally liable for obligations incurred by either of them to meet the ordinary needs of the family, and neither the property regime nor any arrangement between the spouses affects this[6].
Each spouse is fully independent in managing his or her property, as Art. 511 KRO expressly provides. Income from work, investments and business activity likewise goes exclusively to the personal property of the spouse who earned it, and each spouse answers for his or her obligations with his or her own personal property.
The advantages of this regime are full protection of one’s property against the other spouse’s debts, a much simpler division of property on divorce and complete freedom of management. The risk lies with the lower-earning spouse, since there is no mechanism for evening out the difference: on the death of the other spouse or on divorce, that person may find himself or herself in a difficult financial position. Separation of property is a good solution for entrepreneurs, for spouses with different levels of wealth and for people entering a subsequent marriage who wish to protect the interests of their children.
This regime is provided for in Art. 47 § 1 KRO and regulated in Arts. 512-515 KRO. Under Art. 512 KRO, the provisions on separation of property apply accordingly, subject to the further rules on accrued gains and their equalisation. While the agreement is in force, the regime does not differ from ordinary separation of property: property acquired by a spouse before and after the wedding remains personal property and is managed by that spouse. The exception in Art. 30 § 1 KRO continues to apply. The special rules come into play when the regime ends, for example on divorce.
Accrued gains (dorobek) are defined as the increase in the value of a spouse’s property after the marital property agreement was concluded (Art. 513 § 1 KRO). The spouses may define in the agreement which items are disregarded in calculating accrued gains, or rely on the default rules in Art. 513 § 2 KRO. Under those rules, the calculation disregards property acquired before the agreement and the items listed in Art. 33(2), (5)-(7) and (9) KRO (including property acquired by inheritance, legacy or gift), as well as items acquired in exchange for them. The following are added: the value of gifts made by a spouse (other than gifts to the spouses’ common descendants and small customary gifts to other persons), services rendered personally by one spouse for the benefit of the other spouse’s property, and outlays and expenses made on one spouse’s property from the property of the other. Accrued gains are calculated according to the state of the property at the time the separation of property ends and according to prices at the time of settlement (Art. 513 § 3 KRO).
After the separation of property ends, the spouse whose accrued gains are smaller may demand equalisation by payment or by transfer of a right (Art. 514 § 1 KRO). For important reasons, either spouse may demand a reduction of the equalisation obligation, and if the parties cannot agree on the manner or amount of equalisation, the court decides (Art. 514 §§ 2 and 3 KRO). On the death of a spouse, equalisation takes place between that spouse’s heirs and the surviving spouse. The heirs may demand a reduction of the equalisation obligation only if the deceased had brought an action for annulment of the marriage or for divorce, or had applied for separation (Art. 515 §§ 1 and 2 KRO).
The advantages largely mirror those of ordinary separation of property (protection against the other spouse’s debts, freedom of management), combined with protection for the financially weaker spouse and flexibility as to how accrued gains are accounted for. On the other hand, settlements on divorce are considerably more complex and contentious, valuation becomes an issue, and the amount of the former spouse’s claim is hard to predict. The regime is recommended for couples in which one spouse runs a business and wishes to limit the other’s interference in that property, while preserving an element of fairness on divorce, for instance where one spouse gives up a career to look after the home and the children.
Owner of a family business. Separation of property with equalisation of accrued gains should be considered. The business (whether founded before or after the wedding) and the income from it will be personal property. Full separation, however, could prove unfair on divorce to a spouse who supported the firm or took care of the home. Separation with equalisation appears to be the best compromise: the business stays outside any division of property, while the other spouse’s contribution to family life is recognised. In addition, the flexibility in defining accrued gains, including the possibility of excluding the value of the business from the calculation, leaves considerable room for shaping the terms of any equalisation.
Founder of a technology company. Here full separation of property is recommended. A company founded during the marriage under the statutory community forms part of the joint property and would be subject to division on divorce. Full separation ensures the stability of the business in the event of divorce, which investors particularly value; this cannot be guaranteed under the statutory community, or under separation with equalisation if shares in the company had to be transferred. The technology sector also carries risk, so the agreement protects the other spouse against potential liability for the founder’s debts.
Private equity or venture capital investor. Full separation of property is again the best choice, for reasons of stability, protection of the other spouse’s property, no need for spousal consent to investments and ease of settlement on divorce. Assets such as carried interest or interests in funds and portfolio companies are difficult to value, and valuing them on divorce can be costly and contentious. Alternatively, separation with equalisation may be considered, but with a precisely defined method of calculating accrued gains in order to keep the investments as stable as possible.
Owner of a real estate portfolio. The recommendation depends on how the properties were acquired. Properties acquired before the wedding are personal property even under the statutory community (Art. 33(1) KRO). Separation with equalisation would nevertheless be beneficial: it removes the need for spousal consent to the transactions listed in Art. 37 KRO, which greatly facilitates dealing in and managing real estate, while the equalisation mechanism takes account of the growth in value of the properties and ensures a fair outcome on divorce.
Spouse receiving a large inheritance. An inheritance is personal property whether or not a marital property agreement has been concluded (Art. 33(2) KRO). The income generated by inherited property is different: it enters the joint property under Art. 31 § 2(2) KRO. To keep both the inheritance and the income from it as sole property, the spouses should establish separation of property, or a limited community excluding that income from the joint property.
Spouse limiting a professional career to raise children. The most favourable regime is the statutory community or an extended community. If the estates need to be separated, separation with equalisation of accrued gains is strongly recommended. Full separation offers no protection on divorce, despite what is often a very substantial contribution to the functioning of the family and the upbringing of the children.
Person engaged in a high-risk activity. Separation of property (full or with equalisation) should be considered. Both variants separate the spouses’ estates; the difference between them appears only when the regime ends. It must be remembered, however, that the agreement is not effective against persons who did not know of it, so creditors should be informed (Art. 471 KRO). If a creditor does not know that separation of property has been established, the regime that applied before the agreement, for example the statutory community, governs relations with that creditor.
International family connected with Poland, with assets in several countries. Such a family falls within the scope of the Private International Law Act of 2011. Under Art. 52(1) PPM the spouses may choose the law governing their property relations: the national law of either of them, or the law of the state in which either of them is domiciled or habitually resident. A couple choosing Polish law is subject to the KRO. In that situation, separation of property (full or with equalisation) is recommended. Independent management of personal property, clarity of ownership, protection against the other spouse’s debts and (under full separation) ease of division on divorce are among the advantages of this regime where parts of the estates are located abroad.
A marital property agreement must be concluded in the form of a notarial deed, as Art. 47 § 1 KRO expressly requires, whichever regime the spouses choose. Failure to observe the notarial form always renders the agreement invalid (Art. 73 § 2 KC). An agreement concluded, for example, in ordinary written form is invalid and the existing regime (for example the statutory community) continues to apply. Such an agreement cannot be validated after the event; the only solution is to conclude a new agreement in the required notarial form.
The agreement may be concluded both before the wedding and during the marriage. It may also be amended or terminated at any time, each time in notarial form (Art. 47 KRO). An agreement concluded before the wedding in the required form is valid but produces no effects until the marriage is concluded. If the agreement is terminated during the marriage, the statutory community arises by default, unless the spouses decide to establish another regime (Art. 47 § 2 KRO).
A marital property agreement may be concluded in person or through an attorney, since the law does not require the spouses to act personally (Art. 95 § 1 KC). Concluding such an agreement clearly exceeds ordinary management, so a power of attorney for that specific legal act is required (Art. 98 KC). As to form, under Art. 99 KC the power of attorney must be granted in the same special form as is required for the validity of the act itself, that is a notarial deed. Failure to observe that form when granting the power of attorney again renders any agreement signed on its basis invalid.
Full legal capacity is required to conclude a marital property agreement, which as a rule means having reached the age of 18. One situation deserves attention: marriage by a woman who has reached the age of 16. The guardianship court may permit it for important reasons (for example pregnancy) where the marriage will be in the interest of the new family (Art. 10 § 1 KRO). Before the marriage, however, she remains a person with limited legal capacity (Art. 15 KC), so the validity of a marital property agreement depends on the consent of her statutory representative (Art. 17 KC). She attains majority by marrying and does not lose it even if the marriage is annulled, so she may subsequently conclude and terminate marital property agreements on her own.
A fully incapacitated person cannot conclude a marital property agreement, because such a person has no legal capacity (Art. 12 KC) and any agreement concluded would be invalid (Art. 14 § 1 KC). Nor can such a person marry at all (Art. 11 § 1 KRO). The position of a partially incapacitated person is different. Despite limited legal capacity, such a person may marry[7], although in the case of mental illness or intellectual disability the court’s permission is required (Art. 12 § 1 KRO). A marital property agreement may be concluded, but requires the consent of the curator (Arts. 16 § 2 and 17 KC). It should also be noted that if a spouse is incapacitated during the marriage, separation of property arises by operation of law (Art. 53 § 1 KRO).
A further question is the effect of defects of consent on the validity of the agreement. An agreement concluded in a state excluding conscious or free decision-making (Art. 82 KC), or concluded as a sham (Art. 83 § 1 KC), is absolutely void[8].
A material error as to the content of the agreement (Art. 84 KC) makes the agreement voidable: it remains valid and effective until the mistaken party submits to the other party a written declaration avoiding the legal effects of the declaration of intent made under the influence of error. The spouse has one year from discovering the error to do so (Art. 88 § 2 KC). An agreement concluded under an error fraudulently induced by the other spouse is likewise voidable, but in that case the error need not be material or relate to the content of the agreement (Art. 86 § 1 KC). The rules on avoidance are the same as for error (Art. 88 §§ 1 and 2 KC).
Threat also makes the agreement voidable (Art. 87 KC). The declaration avoiding the effects of the agreement is again made to the other party in writing (Art. 88 § 1 KC), within one year from the moment the state of fear ceased (Art. 88 § 2 KC). Not every form of pressure exerted on a spouse will meet all the elements of a threat, namely unlawfulness, seriousness and the creation of a state of fear. If, however, the pressure had a material influence on the conclusion of the agreement, this may be assessed as contrary to the principles of social coexistence, which would render the agreement absolutely void (Art. 58 § 2 KC).
An agreement establishing separation of property (full or with equalisation) has no retroactive effect. A clause providing that the agreement applies “from the beginning of the marriage” would therefore be invalid: the estates are separated from the conclusion of the agreement, and the joint property accumulated until then continues to exist until it is divided. An agreement extending the community does not operate retroactively either, but it may cover assets the spouses already hold: items that by default belong to personal property can be brought into the joint property. Similarly, the community may be limited in respect of items that form part of the joint property at the time the agreement is concluded.
The moment from which the new regime applies depends on when the agreement is concluded and on its terms. If it is concluded before the marriage, the regime applies from the conclusion of the marriage (for example, if separation of property was agreed, no community arises at all). If it is concluded during the marriage, as a rule it applies from the signing of the notarial deed, unless the agreement specifies a later date (Art. 116 § 1 KC). The same applies to an amendment of an existing agreement. Termination of a marital property agreement takes effect on signing the notarial deed to that effect, and the regime reverts by default to the statutory community, unless the spouses have chosen another regime.
It is advisable to obtain from prospective foreign clients documents concerning:
An apostille is a certificate confirming the official character of a document that is to be used abroad in a state party to the Hague Convention of 1961 Abolishing the Requirement of Legalisation for Foreign Public Documents, to which Poland is a party. If the document is to be used in a state that is not a party to the Convention, traditional legalisation is required[9].
A sworn (certified) translation is one made by a sworn translator entered on the list of sworn translators kept by the Ministry of Justice. The profession is regulated by the Act of 25 November 2004 on the Profession of Sworn Translator; a translation certified with the translator’s seal is accepted by authorities and courts. It is required for translations of, among other things, contracts, notarial deeds and court documents. Under Art. 2 § 3 of the Notaries Act (Prawo o notariacie), notarial acts are performed in Polish; at a party’s request, however, the notary may additionally perform the act in a foreign language, relying either on his or her own command of that language, demonstrated in the manner required of sworn translators, or on the assistance of a sworn translator. Furthermore, under Art. 87 § 1(1) of the same Act, if a person taking part in the act does not know the language in which the deed is drawn up, the notary should translate the deed or other document personally or with the assistance of a translator.
How, in practice, can one secure evidence that a foreign client knew the content of the agreement, understood its effects and concluded it freely?
Under Art. 92 § 3 of the Notaries Act, where a notarial deed concerns a legal act it should contain the content essential to that act, as well as any other statements needed in the circumstances. It is therefore necessary to distinguish the essential elements (essentialia negotii), without which the act is defective, from additional elements (accidentalia negotii), which do not affect the validity or effectiveness of the agreement itself:
Once the essential and optional elements have been identified, it is worth considering which issues will matter most in negotiations:
When drafting the clauses that shape the regime, attention should also be paid to additional provisions that do not create a new regime. Some belong in the deed itself, some in a schedule to the main agreement, and some in an entirely separate agreement.
It is equally worth listing examples of clauses that would be impermissible, risky or potentially ineffective:
Importantly, because of the differences between legal systems, some clauses that are permissible in English or American prenuptial agreements may prove entirely unacceptable in a Polish marital property agreement.
The Overdeck case shows very clearly how destructive it can be for such a wealthy couple to leave property matters unregulated in the event of divorce, not only for the divorcing parties but also for the business and for third parties. Advising wealthy international families should therefore rest on a confident command of private international law and of Polish family, civil and procedural law. Depending on the regime, this means regulating precisely the extension or limitation of the joint property, or defining what counts as a spouse’s accrued gains, while respecting mandatory rules (ius cogens) and aligning the agreement with the needs of the business, so that the parties’ interests are protected as fully as possible.
[1] Forbes, Profile: John Overdeck, https://www.forbes.com/profile/john-overdeck/ [accessed: 28 September 2026].
[2] https://dspace.njstatelib.org/server/api/core/bitstreams/505213d0-5ea7-46c7-bc31-8f92a08b9ff7/content
[3] K. Pietrzykowski [in:] K. Pietrzykowski (ed.), Kodeks rodzinny i opiekuńczy. Komentarz, 9th ed., 2025, Art. 47.
[4] J. Szymczyk-Przewoźna, Najmniej małżeństw i najwięcej intercyz w historii. Niedługo będzie ich 100 tys. rocznie, https://www.rp.pl/w-sadzie-i-w-urzedzie/art45153471-najmniej-malzenstw-i-najwiecej-intercyz-w-historii-niedlugo-bedzie-ich-100-tys-rocznie
[5] K. Pietrzykowski [in:] K. Pietrzykowski (ed.), Kodeks rodzinny i opiekuńczy. Komentarz, 9th ed., 2025, Art. 48.
[6] Judgment of the Court of Appeal in Gdańsk of 31 January 2022, I ACa 943/21, LEX no. 3581589.
[7] Judgment of the Supreme Court of 7 April 1967, I CR 559/66, LEX no. 6135.
[8] P. Sobolewski [in:] W. Borysiak (ed.), Kodeks cywilny. Komentarz, 35th ed., 2026, Arts. 82 and 83.
[9] https://www.gov.pl/web/dyplomacja/apostille-legalizacja-dokumentow
[10] B. Bugajski, M. Domański, K. Gołębiowski [in:] J. Haberko (ed.), Prawo rodzinne i opiekuńcze. System Prawa Prywatnego. Tom 11, 1st ed., 2025, Art. 514 of the Family and Guardianship Code (editorial extract).
[11] E. Rudkowska-Ząbczyk [in:] E. Marszałkowska-Krześ, I. Gil (eds.), Kodeks postępowania cywilnego. Komentarz, 40th ed., 2026, Art. 41.