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Prenup vs. Postnup: Key Differences

Last updated 5 min read

A prenup is signed before marriage; a postnup is signed during it. They cover the same ground — separate property, support, what happens at divorce — but courts apply stricter scrutiny to postnups because married spouses owe each other a fiduciary duty. The substance is similar; the bar for enforceability is higher.

Side-by-side comparison

Factor Prenup Postnup
When signedBefore marriageDuring marriage
Court scrutinyContract-based + fairness reviewStricter — fiduciary duty applies
Both attorneys requiredStrongly recommendedEffectively required in most states
Typical cost$1,500–$7,500$1,500–$8,500
Common timingEngagementAfter business start, inheritance, or major asset shift
Recognized by statesAll 50Most, with varying rules

Prenup or postnup: which should you get?

If you\'re engaged and considering one, get the prenup. Cheaper to obtain procedurally, easier to enforce later, and you avoid the awkwardness of "let\'s sign this thing five years in." For details, see how to get a prenuptial agreement.

If you\'re already married and didn\'t get a prenup, a postnup is a real option — recognized in most US states, used regularly for the situations described above. See our postnuptial agreement guide for the full process.

Frequently asked questions

Are postnups harder to enforce than prenups?
Yes, generally. Courts apply stricter scrutiny because married spouses owe each other a fiduciary duty, which doesn't exist before the wedding. The substantive requirements are similar (writing, disclosure, voluntariness) but the bar for "voluntary" and "fair" is higher.
Can a postnup replace a prenup?
Yes. A valid postnup can amend or replace an earlier prenup. The new agreement just has to satisfy your state's postnup requirements. Many couples sign one specifically to update terms after a major life change.
Which is cheaper, a prenup or a postnup?
Roughly similar, with postnups often slightly higher because of stricter procedural requirements and more complex disclosure (the longer you've been married, the more co-mingled the finances). Both run $1,500–$7,500 for most couples; complex estates run higher.
If we didn't get a prenup, is it too late?
No. A postnup is recognized in most states and serves the same function. Sign it during a calm period in the marriage, not while one spouse is threatening divorce — that's the duress fact pattern.

Postnuptial agreement guide

Full postnup walkthrough.

Do I need a prenup?

If you're still engaged.

Should I get a postnup?

5-question decision tree.

Cost by state

Prenup and postnup price ranges.

What makes prenups (and postnups) invalid

Same factors, stricter for postnups.

Find a family-law attorney

Both kinds of agreement.