Prenup vs Postnup, What Is the Difference?
When you sign it. A prenuptial agreement is signed before the wedding and a postnuptial agreement is signed after it, and in Missouri that timing changes which body of law reviews the document.
Most people expect the prenup vs postnup difference to be about content. It is not. The two agreements can say exactly the same things.
There is also a third document that gets folded into the conversation constantly and should not be, which is the separation agreement. Missouri treats all three differently enough that getting the categories right is the first useful thing anyone can tell you about this subject.
What Are the Three Missouri Documents?
A prenuptial agreement, a postnuptial agreement and a separation agreement, distinguished by what the couple intended when they signed.
- Prenuptial agreement. Signed before the wedding, by two people who are not yet married. Missouri courts also call this an antenuptial agreement and the two words mean the same thing. Governed by case law, not by statute, because Missouri never adopted a premarital agreement act. Senate Bill 998 would have created Sections 452.615 through 452.660 in 2010 and those numbers remain vacant in Chapter 452
- Postnuptial agreement. Signed during a marriage that both people intend to continue. Also governed by case law, and by less of it
- Separation agreement. Made attendant upon a separation or a dissolution, meaning the marriage is ending and both people know it. This one has a statute, Section 452.325 RSMo
The line between the second and the third is intent, not the calendar. Two documents that look nearly identical can be reviewed under different frameworks depending on whether the couple was trying to stay together or trying to separate when they signed. That distinction sits underneath the whole prenup vs postnup question and it is the first thing a court asks.
Which One Do I Need?
Whichever one matches where you actually are, and the answer is usually obvious once the three are laid out.
- Engaged and not yet married. A prenuptial agreement. This is the cleanest of the three because nothing has been acquired jointly yet
- Married, staying married, and something changed. A postnuptial agreement. A business started, an inheritance received, one spouse leaving work, a second marriage with children from a first
- Married and the marriage is ending. A separation agreement, which is the document that resolves the actual case
- Married, in a rough patch, and trying to get past it. Still a postnuptial agreement. This version is sometimes called a reconciliation agreement and it is covered below
One thing worth saying to the person in the second category. A great many people asking the prenup vs postnup question believe the window closed at the wedding. It did not. Our page on prenuptial agreements in Missouri covers the first document in full, and our page on legal separation covers the third.
Does Missouri Treat a Prenup and a Postnup Differently?
It applies the same standard to both, and the Missouri decision that says so had to reject an argument that they should be treated differently.
In Lipic v. Lipic, 103 S.W.3d 144 (Mo. App. E.D. 2003), the wife argued that an agreement signed to keep a marriage together was different in kind and should be void as against public policy. The Eastern District answered that “we do not believe that post-nuptial agreements are against public policy in Missouri,” and applied the antenuptial standard to the postnuptial agreement in front of it.
That standard requires the agreement to be entered into “freely, fairly, knowingly, understandingly and in good faith and with full disclosure.”
So the prenup vs postnup difference is not the test. It is the weight of authority behind each. Missouri has a substantial body of prenuptial case law running from Darr v. Darr, 950 S.W.2d 867 (Mo. App. E.D. 1997) through Potts v. Potts (Mo. App. W.D. 2010) and Penrod v. Penrod (Mo. App. E.D. 2021). It has considerably less on postnuptial agreements.
That is a fair thing to know before relying on one, and it is not a reason to avoid one. Thin authority is not adverse authority, and the leading Missouri case came out in favor of enforcement.
Why Does a Separation Agreement Get Its Own Statute?
Because it resolves a case that is already in front of a court, so the legislature gave the court a review standard.
Section 452.325 RSMo authorizes spouses to enter a written separation agreement covering maintenance, the disposition of property, and the custody, support and visitation of their children.
Then subsection 2 does the important part. The terms of a separation agreement, “except terms providing for the custody, support, and visitation of children, are binding upon the court unless it finds, after considering the economic circumstances of the parties and any other relevant evidence produced by the parties, on their own motion or on request of the court, that the separation agreement is unconscionable.”
Read what that actually gives you. A negotiated agreement binds the court unless it is unconscionable, which is a far lower bar to clear than the just division standard a judge applies to a contested case under Section 452.330 RSMo.
That is why settling gives you more control over the outcome than trying the case does, and it is part of why mediation resolves financial issues more privately than a courtroom. Our FAQ on dividing marital property covers the standard a judge applies instead.
What About a Reconciliation Agreement?
Missouri does not treat it as a separate category, and it collapses into the postnuptial one.
The name describes the consideration rather than the document. The couple is in trouble, one or both want to stay, and the agreement is part of what makes staying possible.
Lipic’s reasoning is what does the work here. The court wrote that “the pressures involved when one party to an ante-nuptial agreement wants to get married are at least similar to the pressures involved when one party wants the marriage to continue.” Pressure exists in both settings, so its presence alone is not the thing that separates a valid agreement from an invalid one.
There is no separately reported Missouri line of authority on reconciliation agreements, and Missouri courts have not squarely decided whether the label changes anything about how one gets reviewed. What is different is practical rather than legal. These get signed at the least calm moment in a marriage, which makes the fairness of the process the part most worth being careful about.
Which One Is Harder to Enforce?
Not the one most people guess.
The instinct in any prenup vs postnup comparison is that the prenup is the sturdy one and the postnup is the shaky one, because the prenup came first and feels more traditional. The picture is more mixed than that.
- The separation agreement has the strongest footing, because a statute tells the court what to do with it
- The prenuptial agreement has the deepest case law, which cuts both ways. More authority supporting enforcement, and more reported examples of one failing
- The postnuptial agreement has the thinnest authority, and the leading Missouri case came out in favor of enforcement
The more useful way to think about it is that the document type is rarely what decides the outcome. Disclosure, timing and whether each person understood what they were signing decide it, and those apply to all three.
What Is the Same Across All Three?
Three things, and they are the three that matter most.
None of them can decide custody or child support. Section 452.325.2 RSMo carves out “terms providing for the custody, support, and visitation of children” from what binds a court, and Section 452.325.6 RSMo repeats the carve out. Two adults can contract about their own money. A child’s right to support is not theirs to sign away.
All three need to be in writing and signed. An understanding about who keeps the house is not an agreement, it is a memory, and two people rarely have the same one.
And all three get better with complete disclosure. In Darr the Eastern District looked at whether the spouse was substantially advised of the other spouse’s property or otherwise had knowledge of the relevant facts, which is a more forgiving formulation than the words full disclosure suggest. That is a description of what has survived review after the fact, not a target to aim at. A complete schedule of what each person owns removes the disclosure argument entirely and forces any future challenge onto much harder ground.
Where a business is involved that schedule is the hard part, and our page on divorce for business owners covers why. Our FAQ on whether a business is marital property covers what the agreement is actually allocating.
Does a Marital Agreement Decide Maintenance?
It can, and Section 452.325 gives a separation agreement unusual reach over later modification.
Section 452.325.6 RSMo provides that except for terms concerning the support, custody or visitation of children, the decree “may expressly preclude or limit modification of terms set forth in the decree if the separation agreement so provides.”
That is worth knowing on both sides of the table, because certainty is worth a great deal to the spouse paying and a good deal less to the spouse receiving if circumstances get worse. Our spousal maintenance page covers the standard that otherwise applies.
Who Can Help With a Prenup vs Postnup Decision in Missouri?
Picking the right document is usually a five minute conversation. Drafting one that does what you meant takes longer, and it is the part worth paying for.
Bardol Law Firm practices only family law and drafts and reviews marital agreements for couples in St. Louis County, St. Louis City, St. Charles County and Jefferson County. You can read more about property and asset division, about our family law practice, and the rest of our family law questions and answers.
You should not have to chase your attorney for basic updates. Every client here has a named paralegal on the file, and we generally return calls within one business day.
Family Law, Simplified.
If you are not sure which of the three you need, that is exactly the right question to bring to a first conversation. Contact Bardol Law Firm or call 314.918.0100 to talk it through.
This page is general information about Missouri law and is not legal advice. Every case turns on its own facts. The choice of a lawyer is an important decision and should not be based solely upon advertisements.