California Postnuptial Agreement: Requirements, Example, and Taxes

A California postnuptial agreement is a written contract that spouses sign after they are already married to redefine who owns what, how debts are divided, and what happens financially if the marriage ends or one spouse dies. California gives couples the right to alter their default community property rules through a written marital property agreement under Family Code Section 1500, but because you are already married when you sign, the document has to clear a higher fairness bar than a prenup.¹

There is no dedicated postnuptial statute in California. Prenups have their own framework under the Uniform Premarital Agreement Act (Family Code Sections 1610–1617). Postnups instead run on a combination of general contract law, the spousal fiduciary duty rules in Section 721, and the property transmutation requirements in Sections 850–853. That mix is why postnups face closer scrutiny than prenups, and it shapes almost everything else about how these agreements work.

What a California Postnuptial Agreement Can Do

Reclassify Property Between Spouses

The most common reason couples sign a postnup is to change how property is characterized. California is a community property state, so earnings and assets acquired during the marriage generally belong to both spouses equally. Family Code Section 850 lets spouses override that default by converting community property into one spouse’s separate property, turning separate property into community property, or transferring separate property from one spouse to the other.²

These reclassifications are called transmutations. Section 852 requires an express written declaration signed by the spouse whose interest is being reduced. A vague reference in an email or a casual conversation does not qualify. If the transmutation involves real estate, the declaration also needs to be recorded with the county to protect against third-party claims.³

Couples often use transmutation to keep a family business, an inheritance, or a premarital home classified as separate property even after funds from both spouses have flowed into it. Without an agreement, commingling can blur the line between separate and community property in ways that are expensive to untangle in a divorce.

Allocate Debts

A postnup can assign responsibility for existing and future debts between the spouses. Credit card balances, student loans, and business liabilities can be placed on one spouse’s side of the ledger. That allocation controls how the debts are handled between the two of you. It does not bind creditors who were not party to the agreement.

Address Spousal Support

Spousal support provisions are permitted but face heavy judicial scrutiny. A court reviewing a postnuptial waiver of support will look at whether the waiving spouse had independent counsel, whether the waiver leaves that spouse in dire financial shape, and whether circumstances changed dramatically after signing. A waiver that looked reasonable when both spouses earned similar incomes may be found unconscionable if one spouse later left the workforce to raise children. Courts can refuse to enforce support waivers that produce an unfair result at the time of divorce.

Coordinate With an Estate Plan

A postnup can waive or limit a spouse’s rights to the other’s estate at death, establish how life insurance proceeds are distributed, or clarify which assets pass through a trust versus probate. Any inheritance waiver should be drafted alongside your will or trust so the two documents don’t contradict each other and invite litigation later.

What a Postnup Cannot Do

California has no statute listing what a postnuptial agreement cannot include the way Section 1612 does for prenups. Courts instead apply general contract law and public policy.⁴

Child support cannot be limited by private contract. A judge sets support based on the child’s needs and both parents’ incomes, regardless of what the parents agreed between themselves.
Child custody is a court decision based on the child’s best interests at the time the issue arises. A postnup that tries to lock in a custody arrangement will be ignored.
Unconscionable financial terms, meaning a split so one-sided that no reasonable person would agree to it, can get the whole agreement thrown out.
Lifestyle or personal conduct clauses, such as penalties for weight gain or social media behavior, generally aren’t enforceable. California courts treat postnups as financial contracts.
Creditor rights are not affected. If your agreement reclassifies community property as one spouse’s separate property, creditors can still pursue the asset to collect debts that predate the change. Courts are especially skeptical of transfers made after a creditor has filed a claim or threatened suit.

Why Postnups Face a Higher Bar Than Prenups

At the time a postnup is signed, the spouses already owe each other a fiduciary duty of the highest good faith and fair dealing under Section 721. The California Supreme Court has recognized that this duty makes postnups subject to stricter scrutiny than prenups. When one spouse gains an advantage under the agreement, that spouse carries the burden of proving the deal was not the product of undue influence. With a prenup, the challenging spouse usually bears the burden.⁵

This burden flip is the single most important legal distinction between the two types of agreements. The spouse who benefits has to justify the terms, not the other way around.

Requirements for a Valid Agreement

Every California postnup has to clear several practical hurdles to be enforceable.

In writing and signed by both spouses. Oral postnuptial agreements are not enforceable. If any property is reclassified, Section 852 requires an express written declaration accepted by the spouse giving up the interest.
Full financial disclosure. Each spouse must provide a complete and accurate picture of all assets, debts, and income. A hidden bank account or undisclosed business interest can void the entire agreement.
Voluntary. Neither spouse can be pressured, threatened, or coerced into signing. A spouse who signed under duress has a strong argument for setting the agreement aside.
Substantively fair. Courts assess unconscionability both at the time of signing and at the time enforcement is sought.
Independent legal counsel on both sides. Not technically required for a postnup, but the strongest protection against a future challenge. The prenup statute (Section 1615) explicitly requires independent counsel or a written waiver, and courts evaluating postnups give significant weight to whether each spouse had legal advice.

One common misconception: notarization is not legally required for a California postnup. Notarizing the signatures still makes it much harder for either spouse to later claim a forged signature or deny knowledge of the document, and if real estate is being transferred, notarization becomes practically necessary because you will need to record the deed change with the county.

What the Document Looks Like

A California postnuptial agreement typically contains:

Recitals identifying both spouses, the marriage date and location, and the reasons for the agreement.
Financial disclosure schedules, usually attached as Schedule A and Schedule B, listing every asset and debt each spouse owns. Incomplete schedules are the most common reason agreements are thrown out.
Property classification provisions identifying each asset as community or separate, with transmutations spelled out using the express declarations Section 852 requires.
Debt allocation provisions assigning responsibility for specific existing debts and setting rules for future debts.
Spousal support terms, if included, defining whether support will be paid, in what amount, and under what conditions.
General release clauses where each spouse waives certain claims against the other’s separate property or estate.
Signature blocks for each spouse and, if attorneys were involved, for each attorney confirming the review.

Some agreements also include a sunset clause that terminates the agreement automatically after a set number of years unless the spouses renew it. If your agreement contains no sunset clause, it remains in effect indefinitely until both spouses agree in writing to modify or revoke it.

Retirement Accounts Need Their Own Paperwork

Employer-sponsored plans like 401(k)s and pensions are governed by the federal Employee Retirement Income Security Act (ERISA), and federal law overrides state contract law when the two conflict. A postnuptial agreement alone may not effectively waive a spouse’s rights to retirement plan benefits.

ERISA requires a spousal waiver of plan benefits to be in writing, to specify the beneficiary or benefit type being waived, and to be witnessed by a notary or plan representative. Some courts have held that a waiver in a postnup does not satisfy these requirements unless the plan itself recognizes it. If your agreement touches retirement accounts, you will likely need a separate beneficiary designation form filed directly with the plan administrator, and possibly a Qualified Domestic Relations Order (QDRO) if the marriage ends in divorce. IRAs are not subject to ERISA, so waiving IRA rights through a postnup is more straightforward, though you should still update the beneficiary designation on the account to match.

Taxes on Property Transfers Between Spouses

Under Section 1041 of the Internal Revenue Code, no gain or loss is recognized on property transfers between spouses. The receiving spouse takes over the transferring spouse’s tax basis in the asset. The tax bill does not disappear; it is deferred until the receiving spouse eventually sells.⁶

That basis carryover matters. If your spouse transfers a rental property with a basis of $200,000 but a current value of $600,000, the transfer itself triggers nothing, but you inherit $400,000 of built-in gain when you sell. Postnups that account for this value assets on an after-tax basis rather than market value.

Gift tax is not typically a concern for transfers between U.S. citizen spouses because the unlimited marital deduction applies. The major exception: if the receiving spouse is not a U.S. citizen, that deduction does not apply, and transfers may be subject to annual gift tax limits. Section 1041’s tax-free treatment also does not extend to transfers involving a nonresident-alien spouse or certain transfers in trust where liabilities on the property exceed the transferor’s basis.⁶

Modifying, Revoking, or Moving Out of State

A postnup is not permanent unless you want it to be. Both spouses can agree to modify specific terms or revoke the whole agreement, but any change has to be in writing and signed by both. One spouse cannot unilaterally alter or cancel it. Any amendment should follow the same formalities as the original: updated financial disclosure, voluntary execution, and ideally independent counsel. Life events like a birth, a significant inheritance, a career change, or a home purchase are good triggers for a review.

Relocating to another state complicates enforcement. States vary in how they treat postnuptial agreements. Some apply the same standards as prenups; others impose stricter requirements. A choice-of-law clause specifying that California law governs helps but does not guarantee the new state will honor every provision. A court elsewhere may refuse to enforce terms that violate its own public policy. If you are planning a move, have a family law attorney in the new state review the agreement.

How Postnups Get Challenged

If a divorce or death brings the agreement before a judge, the spouse who benefits typically has to prove it was negotiated fairly. The grounds that most often succeed are:

Incomplete financial disclosure. Hidden assets, an undervalued business, or omitted debts can void the agreement entirely. The attached schedules get examined closely.
Lack of independent counsel. A spouse who signed without a lawyer has a credible argument that they did not understand what they were giving up.
Duress or undue influence. An agreement signed during a marital crisis, such as when one spouse threatened divorce unless the other signed, is vulnerable. Timing and circumstances matter.
Unconscionability at signing or at enforcement. An agreement that strips one spouse of essentially all marital property while the other keeps everything is unlikely to survive.
Ambiguous language. Vague terms or internally contradictory provisions give a court reason to set aside the unclear sections or the whole document.

Including provisions a court cannot enforce is more than wasted space. A clause egregious enough to taint the negotiation can give a judge reason to question whether the whole agreement was entered in good faith.

Cost and Finalizing

Once terms are finalized and both spouses have had independent counsel review the document, both sign the agreement and each schedule. Notarizing the signatures, while not legally required, adds authentication that is difficult to challenge later. If the agreement transmutes real estate, record the relevant documents with the county recorder’s office to put third parties on notice.³

Store the original in a secure location like a fireproof safe or a bank safe deposit box, and have each spouse and attorney retain certified copies. If retirement accounts are involved, file updated beneficiary designations with each plan administrator promptly after signing. Legal fees for drafting and reviewing a postnuptial agreement in California typically range from around $1,000 for a straightforward agreement between spouses with modest assets up to several thousand dollars for complex agreements involving businesses, multiple properties, or significant separate property holdings.

1
California Legislative Information. California Code FAM 1500-1503 – Marital Property Agreements
2
California Legislative Information. California Code FAM 850 – Transmutation of Property
3
California Legislative Information. California Code FAM 852 – Transmutation of Property
4
California Legislative Information. California Code FAM 1612 – Content of Premarital Agreement
5
California Legislative Information. California Code FAM 721 – Relation of Spouses
6
Office of the Law Revision Counsel. 26 USC 1041 – Transfers of Property Between Spouses or Incident to Divorce