Postnuptial Agreement in Florida: What the Law Requires and Why Full Disclosure Comes First

By Aaron Thomas, Esq. · Updated October 26, 2026

Florida enforces postnuptial agreements, but they are judged by a different test than prenups. Under Casto v. Casto, a postnup that is unfair or unreasonable to one spouse is presumed to rest on concealment or a lack of knowledge, and it stands only if the other spouse proves full, frank disclosure or the challenger’s general knowledge of the finances.

Key Takeaways

• Florida enforces postnuptial agreements. They are governed by case law, specifically Casto v. Casto, not by the premarital agreement statute, Fla. Stat. § 61.079.
• Casto’s test is more demanding than the prenup statute’s. A postnup can be challenged for being unfair or unreasonable, not only unconscionable, and once unfairness is shown the burden shifts to the spouse defending it to prove disclosure or the other spouse’s general knowledge of the finances.
• The difference matters most on disclosure. A Florida prenup can survive without strict disclosure unless unconscionability is also shown. A postnup that a court finds unfair or unreasonable cannot rely on that: it survives only if the spouse defending it shows full disclosure or the other spouse’s general knowledge of the finances.
• Independent counsel for each spouse is strongly advisable, and signing formalities can depend on what the agreement covers, so an attorney should confirm what applies.
• A postnup can be signed at any point in a marriage. What matters legally is that it is signed freely and is either fair to both spouses or backed by disclosure, which is why complete, current disclosure and enough time to decide are the best protection.

Does Florida Allow a Postnuptial Agreement?

Yes. Florida courts enforce postnuptial agreements, which define what belongs to each spouse and what happens to assets and debts if the marriage ends. The source of the rule is not the premarital agreement statute. That statute, Fla. Stat. § 61.079, governs agreements signed before the wedding. For agreements between spouses who are already married, the controlling authority is Casto v. Casto, 508 So. 2d 330 (Fla. 1987).

A postnup can be signed at any point in a marriage, whether a few weeks after the wedding or decades in. Couples sign them after an unfinished prenup, when a business takes off, when money has become a source of conflict, or simply to put in writing what they have always assumed. The Florida standard does not set a deadline. It sets a bar for how the agreement is made.

Why Florida Treats a Postnup Differently From a Prenup

Under Florida’s premarital agreement statute, an agreement is unenforceable only if the challenger proves one of three grounds: it was not signed voluntarily; it was the product of fraud, duress, coercion, or overreaching; or it was unconscionable when signed and, before signing, the challenger did not receive fair and reasonable disclosure, did not waive disclosure in writing, and did not have and could not reasonably have had adequate knowledge of the other party’s finances. Disclosure is not strictly required for a prenup to be valid unless it is paired with unconscionability. The burden sits on the person challenging the agreement.

Casto supplies a different test. A postnup can be set aside if it was reached through fraud, deceit, duress, coercion, misrepresentation, or overreaching. It can also be set aside if it makes an unfair or unreasonable provision for the challenging spouse, given the circumstances of the parties. Once a court finds that kind of unfairness, it presumes concealment or a lack of knowledge, and the burden shifts to the spouse defending the agreement to prove a full, frank disclosure before signing or that the challenging spouse had a general and approximate knowledge of the property and income. The prenup statute requires unconscionability and keeps the burden on the challenger; Casto’s trigger is unfairness, and the burden can shift. That is why disclosure is the strongest protection a postnup has, even though Casto does not make it a requirement for every agreement.

What Full Disclosure Means in Practice

Full disclosure means each spouse gives the other a complete and current picture of their finances before signing. That covers assets, debts, income, and accounts, including retirement accounts, business interests, real estate, and anything held in a trust or an entity. It is backed by documents, not summaries: recent statements, tax returns, and current valuations where a value is not obvious.

Two details separate a strong disclosure from a weak one. It has to be current, because a schedule prepared months earlier may no longer describe the finances. And it has to be reviewable, meaning the other spouse actually receives it and has time to read it before signing. The record that shows both of those things happened is what an agreement leans on if it is ever challenged.

What the Stricter Review Means for Drafting

A stricter review changes what a careful agreement looks like. The terms should be fair and reasonable on their face, and lopsided terms should be explained by the agreement itself, such as a larger share to a spouse who contributed more to an asset. Each spouse should have their own attorney, which is not required but is one of the clearest ways to show that each person understood what they were signing. Both should have enough time to read, ask questions, and decide, and nobody should be signing under an ultimatum.

If the agreement waives rights at death, such as the elective share, intestate share, homestead, exempt property, or family allowance, Fla. Stat. § 732.702 requires it to be signed in the presence of two subscribing witnesses, the same rule that applies to a prenup with those waivers. For a waiver signed after marriage, the statute adds a requirement a prenup does not have: each spouse must make fair disclosure of their estate to the other. Postnups are enforceable in most states, though the rules differ widely, so this section describes Florida only. A postnup that is enforceable in court in Florida looks like a strong prenup, with the added weight of complete disclosure.

Getting a Florida Postnup

The process begins with a consultation to understand your situation and goals, followed by full financial disclosure from both spouses, drafting, a round of review with each spouse’s own counsel, and signing when you are both ready. Prenups.com handles postnups for a fixed fee with no hourly billing, and the flat-fee pricing is published in full. Prenups.com’s Florida page covers the firm’s Florida work, and Florida’s prenup requirements are covered separately for couples who are still before the wedding.

If you are weighing a postnup, you can schedule a consultation with a licensed attorney to talk through whether it fits and what Florida’s standard means for your situation. For the broader picture of how postnups work, see the full guide to postnups.

Frequently Asked Questions

Sources

• Fla. Stat. § 61.079 (premarital agreements)
• Casto v. Casto, 508 So. 2d 330 (Fla. 1987)
• Fla. Stat. § 732.702 (waiver of spousal rights)