Married without a prenup — or married with one that no longer fits? Florida law lets spouses make a binding financial agreement during the marriage: the postnuptial agreement. It can do nearly everything a prenup does, but it lives under different law, carries stricter disclosure expectations, and gets attacked in different ways. Here is how postnups work in Florida, when they are the right instrument, and how we build ones that hold.
A different statute — actually, no statute at all
Florida's premarital agreement act, section 61.079, governs only agreements made before marriage. Postnuptial agreements are creatures of Florida common law, tested under the framework the Florida Supreme Court set out in Casto v. Casto: a spouse challenging a postnup can set it aside by proving it was the product of fraud, deceit, duress, coercion, misrepresentation, or overreaching — or by showing the agreement makes an unreasonable provision for that spouse, which raises a presumption of concealment the defending spouse must rebut with proof of full disclosure or the challenging spouse's independent knowledge of the finances. Notice what that second route means in practice: a lopsided postnup shifts the burden onto the spouse enforcing it. Disclosure is not merely prudent in a postnup — it is structurally decisive, more so even than in prenups. Between spouses there is also a relationship of confidence the law respects: you are no longer two independent people bargaining before a wedding; you are partners, and courts read candor obligations accordingly.
When a postnup is the right tool
The prenup that never happened. The most common call: the couple meant to sign before the wedding, ran out of runway (wisely refusing a rushed signing), and now wants the agreement done properly. A deliberate postnup, negotiated in calm months rather than wedding-week chaos, is often stronger than the pressured prenup would have been.
The business event. A company is founded, a partner buys in, investors demand clean cap tables, a professional practice grows. A postnup can define the enterprise — and its appreciation and income — as separate, fix a valuation method, and keep a future dissolution out of the operating agreement's way. Business partners and lenders increasingly ask for exactly this.
The inheritance or windfall. Family money arrives or becomes imminent. A postnup can wall it off before commingling blurs it, and coordinate with the family's trust planning — often at the parents' urging, and often paired with our broader marital-agreement planning.
The reconciliation. After infidelity or a near-divorce, spouses sometimes rebuild on renegotiated financial terms — a "reconciliation agreement." Florida enforces these, and they can genuinely save marriages by replacing suspicion with signed clarity. They are also the postnups most likely to be attacked later, so process discipline matters doubly.
The estate-plan alignment. Blended families, children from prior marriages, second marriages later in life: a postnup with waivers of elective share, homestead, and other survivor rights under section 732.702 — which after marriage requires fair disclosure, unlike its premarital counterpart — is frequently the missing piece that makes the whole estate plan actually work.
The prenup tune-up. Amending, ratifying, or updating an existing prenup after marriage is itself a postnuptial act. Stale schedules refreshed, defective execution cured, terms adjusted for children or a new state — see our drafting-mistakes page for what usually needs fixing.
What a postnup can and cannot do
The reach mirrors prenups: property rights and management, division on dissolution or death, alimony (with the same Florida limits — temporary support and fees during a pending case cannot be waived in advance, and no waiver can push a spouse onto public assistance), life insurance, attorney's fees for enforcing the agreement itself, choice of law, confidentiality. The same absolute limits also carry over: child support cannot be bargained away, and time-sharing is decided by the court on best interests when the time comes. One postnup-specific caution deserves its own sentence: an agreement signed while a divorce is secretly planned — one spouse negotiating "reconciliation terms" while counsel drafts a petition — is the classic fraud fact pattern under Casto. Postnups are for building or restructuring a marriage's finances, not for ambushing its end.
Consideration: the quiet technical requirement
A prenup's consideration is the marriage itself; a postnup needs its own. In practice this is a drafting detail solved with mutual promises, waivers, and exchanges inside the agreement — but it is one more place where self-drafted documents stumble, particularly one-way agreements where a spouse appears to give up rights and receive nothing. We build reciprocity into the structure both because contract law wants it and because a court applying Casto's "unreasonable provision" test is measuring exactly that balance.
Process: how we build a postnup that survives
Everything on our disclosure and execution pages applies with the volume turned up. Full, documented, current disclosure from both spouses — schedules, statements, returns — because the burden-shifting presumption makes thin disclosure fatal in a way prenup law forgives less often. Genuine independent counsel on both sides; between spouses, an unrepresented party is an even richer overreaching argument than between fiancés. Unhurried negotiation in writing. Execution with two subscribing witnesses and a notary — the 732.702 waivers demand the witnesses, and the evidentiary habit costs nothing. Duplicate originals vaulted separately, estate plan and beneficiary designations reconciled, ERISA spousal consents signed on plan forms (finally possible, since you are now spouses — this is where prenup follow-through actually lands). And where the postnup amends a prenup: recite the original, state exactly what changes, and execute with full formality, so the two documents read as one coherent record.
Common questions
Yes — Florida courts have enforced marital agreements between spouses for decades under the Casto framework. The honest caveat is that postnups are examined closely: the challenging spouse has two routes of attack, and one of them shifts the burden to the enforcing spouse when the deal looks unreasonable and disclosure was weak. Enforceability is earned through process — disclosure, counsel, clean execution — far more than through clever wording.
Not too late — this is exactly what postnups are for, and couples in stable marriages often produce better agreements than engaged couples negotiating against a wedding date. You will exchange full current disclosure, each retain counsel, and negotiate without a countdown clock. Many of our strongest agreements are postnups signed years into the marriage, when both spouses know precisely what they are protecting and why.
A reconciliation agreement can remove the financial fear from staying — guaranteed terms, security for the wronged spouse, consequences defined in advance — and for some couples that clarity is what makes reconciliation possible. Two disciplines keep it honest: both spouses need independent counsel and full disclosure, and neither can be secretly planning a divorce while signing. We have seen these agreements anchor rebuilt marriages; we have also litigated the ones signed as ambushes. The difference was always the process.
If you are engaged with time to do it right, a prenup: section 61.079's enforcement test is well-defined and the burden rests squarely on the challenger. If you are already married, the comparison is moot and the postnup is the tool — built to the stricter Casto standard. If you are engaged with no time, a deliberate postnup after the wedding usually beats a rushed prenup before it. The ranking is really about process quality, not instrument type.
Florida does not mandate it, and our advice is unequivocal: yes. Spouses stand in a confidential relationship, which makes overreaching arguments easier, not harder, when one side was unrepresented. Two lawyers convert the agreement into a documented negotiation between advised partners — and under Casto's burden-shifting, that record is frequently what decides the case. The review-side engagement works the same as for prenups; flat fee, direct with the attorney.
Married, and ready to put the finances in writing?
Postnup drafting, review, and prenup amendments — flat fees quoted plainly. Call (407) 749-1034 or request a confidential consultation.
General information about Florida law — not legal advice, and no attorney-client relationship is created by reading it. Authorities referenced include Casto v. Casto, 508 So. 2d 330 (Fla. 1987), §§ 61.079, 732.702, Fla. Stat., and Belcher v. Belcher, 271 So. 2d 7 (Fla. 1972) (verified July 2026). Every situation turns on its own facts.