A postnuptial agreement is harder to enforce in California than a prenuptial, not easier. This surprises most couples. Once you are married, the law holds you to a higher standard of honesty towards your spouse, and this standard shapes everything about whether your agreement will survive a divorce.

What a Postnuptial Agreement Actually Is

A postnuptial agreement is a written contract that two spouses sign after their wedding. It determines how property, debts, and spousal support will be managed during the marriage and in the event of the marriage’s dissolution. California law explicitly permits these arrangements. Under Family Code § 1500, spouses may alter the property rights that the statute otherwise assigns to them.

Couples often consider a postnuptial agreement when their financial situation changes:

• One spouse starts a business and its value grows rapidly.
• An inheritance arrives that needs to be kept separate from the other spouse’s assets.
• One partner takes on substantial debt that the other does not want to be responsible for.
• A prenup has never been signed, and the couple wishes to address this now.

The Fiduciary Duty Changes Everything

Here is the part that catches people off guard. Family Code § 721 says that spouses owe each other a fiduciary duty, which is the highest duty of good faith and fair dealing. The same kind of business partners and trustees have to do. You have to disclose your full financial situation. You cannot take advantage of your spouse’s trust.

Because of this duty, California courts treat prenups with great skepticism. When an agreement benefits one spouse at the expense of the other, the law assumes undue influence. The spouse who benefits then bears the burden of proving that the deal was fair, informed, and voluntary. Prenups do not carry such a presumption.

What It Takes to Hold Up in Court

To survive a California divorce, a postnuptial agreement must generally meet several requirements:

• It must be in writing. Oral agreements regarding property do not count. Family Code § 852 requires a written declaration of intent to change the nature of property.
• There must be full financial disclosure. Hiding assets violates the fiduciary duty and can invalidate the entire agreement. This is non-negotiable.
• The agreement must be voluntary. There should be no pressure or ultimatums the night before a major transaction.
• When signed and enforced, the agreement must be fair. An agreement leaving one spouse with nothing could be deemed unconscionable and thrown out.

Independent lawyers on both sides are more important than people expect. California does not require separate counsel for every postnup, but a spousal support waiver is only enforceable if the waiving spouse has their own attorney. And when only one spouse is represented, a judge will be more likely to believe that the other spouse did not understand what they were signing.

One thing a postnup can never do is to lock in child custody or child support. These decisions belong to the court and are based on the best interests of the child, regardless of what two parents may have agreed to in writing.

A Postnup Is Only as Strong as the Way It Was Built

A well-drafted postnuptial agreement can protect a business, keep an inheritance separate, and provide financial clarity for a marriage. A rushed agreement can collapse during divorce and leave you vulnerable at the worst possible time. The difference lies almost always in drafting and disclosure.

If you’re considering a post-nuptial agreement, or if you’re facing divorce and wondering whether the one you signed will hold up, talk to an attorney who knows how California courts really scrutinize these documents. At Roberts & Zatlin, we draft, review, and challenge prenuptial agreements throughout the Inland Valley. Contact us to schedule a free consultation and find out what your options are.