What a postnuptial agreement is

When couples marry, they expect the marriage to last. Planning for the possibility that it will not, or for the certainty that one spouse will die first, is still worth doing, and one tool for it is the Illinois postnuptial agreement. A prenuptial agreement is signed before the wedding. A postnuptial agreement, or "postnup," is signed after it. It lets spouses define their rights and obligations as to property, debts, income and support if the marriage ends through divorce or death. In practice it is a roadmap for the financial side of the marriage: which assets are separate, which are shared, who is responsible for which debts, and what each spouse will and will not claim from the other.

Because the spouses are already married, a postnup does not create any new status. It supplements rights that already exist. Couples use one to protect a family business, to deal with an inheritance, to settle what happens to a house that one family helped pay for, or simply to write down who keeps what. Illinois law recognizes the result: property "excluded by valid agreement of the parties, including a premarital agreement or a postnuptial agreement" is non-marital property under the Illinois Marriage and Dissolution of Marriage Act (750 ILCS 5/503(a)(4)). The sections below explain the legal framework, the usual terms, the limits, and the practical steps. Our prenuptial and postnuptial agreements page explains how we draft one.

A prenup is governed by the Illinois Uniform Premarital Agreement Act (750 ILCS 10). A postnup is not: the Act covers only agreements made in contemplation of marriage. Illinois courts treat a postnup as a contract between spouses, enforced under ordinary contract principles, and they look at it more closely than an ordinary contract because spouses owe each other a duty of good faith. For an Illinois postnuptial agreement to be enforceable, it must meet several criteria. Understanding them is the strongest reason for careful drafting.

Full and fair disclosure

The most basic requirement is full and fair disclosure. Each spouse must provide complete information about their assets, income and liabilities: bank accounts, investments, real estate, business interests and personal debts. Omitting or hiding a significant asset can make the agreement unenforceable. If one spouse fails to reveal a substantial inheritance or a business holding, the court may refuse to enforce the agreement when it is finally tested.

Disclosure is what lets both spouses sign with their eyes open. To document it, couples attach financial statements or asset schedules to the agreement. In the main Illinois postnup case, In re Marriage of Tabassum and Younis, 377 Ill. App. 3d 761 (2d Dist. 2007), the court enforced an agreement in which the spouses stated that they were sufficiently aware of each other's finances and expressly waived further disclosure, because the spouse resisting the agreement admitted he had learned nothing new afterwards. Do not plan around that holding. Attach the schedules.

Voluntary execution

An enforceable Illinois postnuptial agreement must be signed voluntarily, without coercion or undue pressure. Courts examine whether one spouse compelled the other to sign, for instance by threatening divorce, withholding financial support, or using access to the children as leverage. Evidence of free will, such as correspondence showing open negotiation and time to consider the terms, demonstrates voluntariness. If the court finds that a spouse signed under duress, the agreement is set aside. In In re Marriage of Richardson, 237 Ill. App. 3d 1067 (1st Dist. 1992), the wife's first lawyer told her not to sign, the husband's lawyer then found her a different lawyer, and the court treated the resulting signature as the product of duress.

Consideration

This is where a postnup differs from a prenup in Illinois. A premarital agreement is enforceable without consideration under the Act (750 ILCS 10/3); the marriage itself is the exchange. A postnup is an ordinary contract and needs consideration: each spouse must give or give up something. In Tabassum the trial court refused to enforce the agreement because the wife's only "consideration" was a promise to stay married, which it called past consideration. The appellate court reversed, holding that her forbearance from filing for divorce, even for a limited period, was consideration, and that the spouses did not have to be separated for that to be true. A mutual exchange of property rights, a waiver of a claim the other spouse would otherwise face, or a transfer of an asset are the usual forms. The agreement should say in plain words what each side is giving.

Conscionability

The agreement's terms must be conscionable: they cannot be grossly unfair or one-sided. Illinois courts look at two things. Procedural unconscionability is an impropriety in the way the contract was formed that deprived one party of a meaningful choice. Substantive unconscionability is terms so one-sided that they oppress or unfairly surprise the other party, or an overall imbalance in the obligations and rights the bargain imposes. In Richardson the agreement gave the wife about 7.55 percent of the assets on the balance sheet, and it was struck down. An agreement that leaves one spouse with nearly all of the marital estate and the other with negligible resources is the kind of term a court will not enforce. The purpose of a postnup is clarity, not stripping one party of everything.

A fair agreement can still be flexible. Couples may agree that each keeps their separate property while splitting marital assets evenly, or adjust the division if one spouse gives up a career to support the family. Balance improves the odds of enforcement.

Independent representation is not strictly required, but it is strongly recommended, and one lawyer cannot represent both spouses to an agreement between them. When both spouses consult their own lawyers, the risk of misunderstanding falls. Independent counsel reviews the agreement, explains each spouse's rights, and suggests revisions. Without separate lawyers, a spouse may later claim they did not understand the terms, and the agreement becomes the subject of litigation rather than a way to avoid it. Each spouse should have their own lawyer, and we recommend it in every case.

Proper execution

An Illinois postnuptial agreement must be in writing and signed by both spouses. Oral agreements and informal promises are not enough. Witnesses and notarization are not required by statute, but they are recommended, because they prove that the agreement exists and was signed by the people it names, and they defeat later claims of forgery or fraud.

Common provisions in Illinois postnuptial agreements

A well-drafted postnuptial agreement addresses a handful of core issues. Every family is different, but most Illinois postnuptial agreements cover property division, financial support, debt allocation and estate planning.

Property division

Illinois classifies assets as marital property or non-marital property. Marital property is generally everything acquired during the marriage; non-marital property includes assets owned before the wedding, gifts and inheritances, and property excluded by a valid agreement (750 ILCS 5/503(a)). A postnup can:

  • Define separate property. List specific assets each spouse owns and declare them non-marital in the event of divorce: a premarital home, family heirlooms, an account funded before the marriage.
  • Specify the division of marital property. Decide whether marital assets split equally or in some other proportion, and how contributions to a business or to the household are valued.
  • Address appreciation of separate property. If a separate asset grows in value during the marriage, say whether the growth stays separate or becomes marital. The statute's default rules on reimbursement are complicated, and an agreement can replace them.
  • Set rules for the marital residence. Say who keeps the home, or that it will be sold and the proceeds divided in stated shares.

Clear property terms remove uncertainty if the marriage ends. They also protect family wealth and make sure each spouse receives what both intended.

Financial support obligations

Spousal maintenance is another area where couples want certainty. A postnup can set out whether and how maintenance will be paid:

  • Waiving maintenance. Some couples agree that neither will claim maintenance.
  • Limiting duration or amount. The agreement can tie maintenance to the length of the marriage; for example, after a decade of marriage one spouse receives support for a stated number of years.
  • Lump-sum payments. Instead of monthly support, a spouse receives a single payment at divorce.

These terms head off long disputes over support. Courts still review a maintenance provision for fairness, and a waiver that would leave one spouse without the means to support themselves because of a change nobody foresaw is the clause most likely to be challenged.

Debt allocation

The agreement should also deal with existing and future debts, so each spouse knows which liabilities are theirs. It can:

  • Assign responsibility for current debts. Credit card debt used for the household might be split, while business debt stays with the spouse who owns the business.
  • Say how future debts are treated. Couples often agree that each spouse is solely responsible for debts in their own name.
  • Include indemnification. If one spouse assumes a debt, the agreement can require that spouse to reimburse the other if a creditor pursues them anyway.

Settling debt up front reduces surprises and protects both spouses' credit.

Estate planning provisions

Postnuptial agreements often intersect with estate plans. Illinois gives a surviving spouse rights that a will alone cannot remove: a spouse who is left out of a will may renounce it and take one-third of the estate if there are descendants, or one-half if there are none (755 ILCS 5/2-8). A postnup can waive or shape those rights. Common provisions:

  • Waiving inheritance rights. A spouse waives the statutory share so that assets pass to children from a prior marriage.
  • Specifying bequests. The agreement requires certain property to be left to the other spouse or to named beneficiaries.
  • Requiring life insurance. A spouse must carry a policy that secures the obligations the agreement creates.

The agreement is only one piece. The will, any trust and every beneficiary designation must say the same thing, or the designation wins. Our articles on Illinois will requirements and beneficiary designations explain why, and the estate planning hub covers the plan as a whole.

Limitations and considerations

A postnup is not a cure for everything. Its limits are worth knowing in advance.

  • Child-related matters. Provisions on parental responsibility, parenting time or child support do not bind the court. A child's right to support cannot be adversely affected by the parents' agreement, and a court decides parenting issues on the child's best interests regardless of what the parents signed (750 ILCS 5/502(b); 750 ILCS 10/4(b)).
  • Public policy. A provision that encourages divorce, or is otherwise contrary to public policy, will not be enforced. Rewarding a spouse for filing for divorce is the standard example.
  • Changed circumstances. A court may decline to enforce a term that has become unconscionable because circumstances changed dramatically. A maintenance waiver signed by a spouse who later becomes disabled and cannot work is the usual case.

Those limits are the reason for fair, balanced terms that anticipate change rather than ignore it.

Practical steps for Illinois couples

Couples considering an Illinois postnuptial agreement can do several things to make it fair and enforceable:

  • Hire separate lawyers. Each spouse engages independent counsel, so both receive unbiased advice and understand the terms.
  • Exchange full financial disclosure. Attach schedules of assets, liabilities and income, with values and the basis for them. Transparent disclosure prevents later challenges.
  • Document voluntariness. Keep the drafts and the correspondence showing that both spouses negotiated freely and had time to think.
  • Review the agreement periodically. The birth of a child, the sale of a business or a significant change in income is a reason to update it.
  • Work out the tax consequences before signing. Transfers of property between spouses, or between former spouses incident to a divorce, are not taxable events, and the recipient takes the transferor's basis (26 U.S.C. 1041), so a spouse who receives a low-basis asset also receives its built-in capital gain. For agreements executed after 2018, maintenance is neither deductible by the payer nor income to the recipient (IRS Topic 452), which changes the arithmetic of a lump sum against monthly payments. Deciding which asset each spouse keeps, and what each will owe on it later, is where it helps that the lawyer drafting the agreement is also a CPA; see our attorney-CPA page.

These steps increase the chance the agreement will hold up and reduce the chance it is ever litigated.

Frequently asked questions

Are postnuptial agreements enforceable in Illinois?

Yes, as contracts. Illinois courts enforce a postnup that was signed voluntarily, with fair disclosure, for consideration, and whose terms are not unconscionable, and the Marriage and Dissolution of Marriage Act treats property excluded by a valid postnuptial agreement as non-marital (750 ILCS 5/503(a)(4)).

What is the difference between a prenup and a postnup in Illinois?

Timing and the governing law. A prenup is signed before the wedding, is governed by the Uniform Premarital Agreement Act, and needs no consideration. A postnup is signed during the marriage, is governed by contract law, needs consideration, and is scrutinized more closely because the spouses already owe each other duties.

Can a postnup decide child custody or child support?

No. Terms about parenting time, decision-making or child support do not bind the court. The Marriage and Dissolution of Marriage Act makes the terms of a marital agreement binding on the court except those providing for support and the allocation of parental responsibilities (750 ILCS 5/502(b)), and the Premarital Agreement Act says the same for prenups (750 ILCS 10/4(b)). A judge decides those questions on the child's best interests at the time of the divorce. A postnup can record what the parents intend, and a court may consider it, but it cannot make the term binding.

Can a postnup waive my spouse's inheritance rights?

Yes. A surviving spouse's right to renounce a will and take one-third of the probate estate if there are descendants, or one-half if there are none (755 ILCS 5/2-8), can be waived in a valid agreement, which is how couples in second marriages protect children from the first. The waiver has to meet the same tests as the rest of the postnup: full disclosure, voluntary signing and consideration. It also reaches only the probate estate, so the will, any trust and every beneficiary designation must be changed to match, or the designation controls.

Do we each need our own lawyer?

One lawyer cannot represent both of you to an agreement between you, because your interests in the terms are opposed. Illinois does not make separate counsel a condition of validity, but an agreement signed by a spouse who had no lawyer is the one most often attacked as involuntary or unconscionable, and in Richardson the court set aside an agreement after the husband's lawyer had steered the wife to a new lawyer. Each spouse should have independent counsel, and we recommend it in every case.

General information as of September 2, 2025, revised October 4, 2026; not legal advice; laws change; consult a lawyer about your situation.