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Prenup vs. Postnup in Florida: What’s the Difference?

By Nadia Pazos, Family Law Attorney, Pazos Law Group · Updated  ·  ← All blog posts

They sound similar and cover much of the same ground, but a prenuptial and a postnuptial agreement are governed by different bodies of Florida law — and that difference matters if either is ever challenged.

Quick Answer

Governing authority: Fla. Stat. § 61.079(3) (the writing-and-signature formality); Fla. Stat. § 61.079(7)(a) (the grounds for setting an agreement aside).

A prenuptial agreement is signed before marriage and is governed by Fla. Stat. § 61.079. A postnuptial agreement is signed after a couple is already married and is governed by Florida contract law and case law — notably Casto v. Casto, 508 So. 2d 330 (Fla. 1987). Both can define separate versus marital property and set or waive alimony; neither can predetermine child support or custody. In practice, postnups face close scrutiny because spouses already owe each other a duty of good faith.

Which Florida Statute Governs Prenuptial Agreements? (§ 61.079, Uniform Premarital Agreement Act)

Florida prenuptial agreements are governed by Fla. Stat. § 61.079(3) and the rest of the Uniform Premarital Agreement Act. Every proposition below is tied to the pinpoint subsection that supports it. Links go to the official text published by the Florida Legislature.

  • § 61.079(1) — adopts the Uniform Premarital Agreement Act and applies it to proceedings under the Florida Family Law Rules of Procedure.
  • § 61.079(2)(a) — defines a premarital agreement as one between prospective spouses made in contemplation of marriage and effective upon marriage.
  • § 61.079(3) — requires the agreement to be in writing and signed by both parties, and makes it enforceable without consideration other than the marriage itself.
  • § 61.079(4)(a)1.–8. — lists the permitted subjects, including property rights, management and disposition of property, wills and trusts, life insurance death benefits, and choice of law.
  • § 61.079(4)(a)4. — expressly permits the establishment, modification, waiver, or elimination of spousal support.
  • § 61.079(4)(b) — provides that a child’s right to support may not be adversely affected by a premarital agreement.
  • § 61.079(5) — makes the agreement effective upon marriage.
  • § 61.079(6) — allows amendment, revocation, or abandonment after marriage only by a written agreement signed by the parties.
  • § 61.079(7)(a)1. — ground to set aside: the party did not execute the agreement voluntarily.
  • § 61.079(7)(a)2. — ground to set aside: fraud, duress, coercion, or overreaching.
  • § 61.079(7)(a)3. — ground to set aside: unconscionable when executed, combined with the absence of fair and reasonable disclosure, no written waiver of disclosure, and no adequate knowledge of the other party’s finances.
  • § 61.079(7)(b) — allows a court to order support notwithstanding a waiver where the waiver would make a party eligible for public assistance.
  • § 61.079(7)(c) — makes unconscionability a question for the court to decide as a matter of law.
  • § 61.079(8) — limits enforcement where the marriage is determined to be void.
  • § 61.079(9) — tolls the statute of limitations on claims under the agreement during the marriage, while preserving laches and estoppel.
  • § 61.079(10) — confirms the section does not alter the formalities of spousal agreements under §§ 732.701–732.702.
  • § 61.075(6)(b) — makes assets and liabilities excluded by a valid written agreement nonmarital and therefore outside equitable distribution.
  • § 61.08(1)(a) — identifies the forms of alimony an agreement can waive or modify.
  • § 61.30(1)(a) — the child support guidelines remain presumptive regardless of what the agreement says.
  • § 61.16 — governs attorney’s fees in litigation over the agreement.
  • Casto v. Casto, 508 So. 2d 330 (Fla. 1987) — the Florida Supreme Court decision on setting aside marital agreements.
  • § 61.021 — requires 6 months of Florida residency before the dissolution in which the agreement is enforced.
  • § 61.052 — supplies the no-fault ground for the proceeding in which the agreement is applied.
  • § 61.19 — bars entry of the final judgment incorporating the agreement until at least 20 days after filing, absent a showing that the delay would cause injustice.
  • § 61.13(2)(c)1. — time-sharing is fixed by statute and by the child’s best interests; a premarital agreement cannot bind it.
  • § 61.14 — support terms the agreement leaves open remain subject to modification under this section.

Source: Florida Legislature, 2025 Florida Statutes. Fla. Stat. ch. 61 Fla. Stat. ch. 61

“A premarital agreement must be in writing and signed by both parties. It is enforceable without consideration other than the marriage itself.” — Fla. Stat. § 61.079(3)
“An issue of unconscionability of a premarital agreement shall be decided by the court as a matter of law.” — Fla. Stat. § 61.079(7)(c)
“The right of a child to support may not be adversely affected by a premarital agreement.” — Fla. Stat. § 61.079(4)(b)

Answers to the Questions the Statute Actually Decides

Does a Florida prenup have to be notarized under § 61.079(3)?

The statute requires only that the agreement be in writing and signed by both parties. It does not require notarization or witnesses, and it expressly makes the agreement enforceable without consideration other than the marriage itself. Notarization is nevertheless routine practice because it makes execution far easier to prove later.

What can invalidate a Florida prenuptial agreement?

§ 61.079(7)(a) supplies three grounds, and the burden is on the party attacking the agreement: involuntary execution; fraud, duress, coercion, or overreaching; or unconscionability at execution combined with the absence of fair and reasonable financial disclosure, no written waiver of disclosure, and no adequate independent knowledge of the other party’s finances.

Can a prenup waive child support?

No. § 61.079(4)(b) provides that a child’s right to support may not be adversely affected by a premarital agreement. Child support is calculated under the § 61.30(1)(a) guidelines regardless of what the parties agreed before marriage.

Who decides whether a prenup is unconscionable?

The judge, and as a matter of law — that is the express command of § 61.079(7)(c). Unconscionability alone is also not enough; it must be paired with the disclosure failures listed in § 61.079(7)(a)3.

Statutory authority checked against the 2025 Florida Statutes on 6 August 2026.

The Core Difference: Timing and Legal Basis

The obvious difference is when you sign. A prenup is executed before the wedding and only takes effect once you marry. A postnup is executed after you are already married. But the more important difference is the law that governs each.

Why Postnups Face Closer Scrutiny

Before marriage, two people are dealing at arm’s length. Once married, spouses owe each other a duty of good faith and fair dealing, so Florida courts examine postnuptial agreements carefully. Under Casto, a spouse can challenge a marital agreement by showing it was reached through fraud, deceit, duress, coercion, misrepresentation, or overreaching — or, alternatively, that it is unfair or unreasonable given the parties’ circumstances and was signed without adequate financial disclosure. The practical takeaway: full, honest disclosure and independent counsel matter even more with a postnup.

What Each Agreement Can Do

Both a prenup and a postnup can define what is separate versus marital property, direct how assets pass on divorce or death, protect a business or professional practice, allocate debt, and set, limit, or waive alimony. And both share the same hard limit: neither can predetermine child support or a parenting schedule, which Florida courts decide under the best-interests standard in Fla. Stat. § 61.13.

When Couples Use a Postnup

Which Is Stronger?

All else equal, a properly executed prenup rests on a clear statute and is generally the more predictable instrument. A postnup is fully valid and enforceable in Florida, but because it is judged under Casto rather than a checklist statute, the quality of disclosure and process carries even more weight. If you can address these questions before the wedding, a prenup is usually the cleaner path; if life has already moved on, a carefully drafted postnup accomplishes the same goals.

Frequently Asked Questions

Is a postnuptial agreement enforceable in Florida?

Yes. Florida enforces postnuptial agreements. They are governed by contract law and cases like Casto v. Casto, 508 So. 2d 330 (Fla. 1987), rather than the prenup statute. A postnup can be challenged if it was procured by fraud, duress, coercion, or overreaching, or is unfair and was signed without adequate financial disclosure.

What is the main difference between a prenup and a postnup?

Timing and governing law. A prenup is signed before marriage and governed by Fla. Stat. § 61.079. A postnup is signed during the marriage and governed by Florida contract law and case law (Casto v. Casto). Both can address property and alimony but not child support or custody.

Can we turn our prenup into a postnup, or update it after marrying?

You cannot convert one into the other, but a married couple can sign a new postnuptial agreement that updates or replaces the terms of an earlier prenup. The postnup must meet the standards for marital agreements, including fair disclosure and voluntary execution.

Why would a married couple sign a postnup?

Common reasons include: the wedding arrived before a prenup was finished; one spouse later started a business or received an inheritance; the couple is reconciling and wants clear financial expectations; or the postnup supports an estate plan to preserve assets for children from a prior relationship.

Speak With a Florida Prenuptial Agreement Attorney

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This article is general legal information about Florida law and is not legal advice. Whether a prenuptial or postnuptial agreement is enforceable depends on the specific facts, the parties’ disclosures, and the circumstances of signing. Reading this content does not create an attorney-client relationship with Pazos Law Group. Florida law changes over time; please consult a licensed Florida attorney about your situation.