A prenup does not become invalid after 10 years of marriage. No state has a law that voids a prenuptial agreement at any marriage anniversary, and a properly executed prenup is just as enforceable after 20 years as it is after two. The 10-year figure that circulates online refers to a Social Security rule for divorced spouses, not to prenup validity. What can actually weaken an older prenup is something written into the document itself, the way the couple handled money during the marriage, or a dramatic change in circumstances since the signing.
Where the 10-Year Idea Comes From
The 10-year threshold that matters in family law is a Social Security rule, not a contract rule. A divorced spouse who was married for at least 10 years can collect Social Security benefits based on the former spouse’s earnings record.1Social Security Administration. Benefits Planner – If You Are Divorced The divorced spouse must be at least 62, currently unmarried, and not entitled to a higher benefit on their own record.2Social Security Administration. Benefits for Your Divorced Spouse
A prenup cannot waive this right. Social Security benefits are governed by federal law, and a private contract between spouses cannot override them. If your marriage reaches 10 years, the lower-earning spouse is eligible regardless of anything the prenup says. For a spouse who out-earned the other for most of the marriage, this can add up to meaningful money over a lifetime, which is why family lawyers often advise clients approaching the mark to delay a divorce filing until after the anniversary.
So the 10-year number is real, but it does nothing to a prenup. The agreement itself keeps running.
Sunset Clauses: The Only Way a Prenup Expires on a Timeline
The one situation where a prenup actually expires on a set date is when the couple built an expiration mechanism into the agreement itself. These “sunset clauses” cause the entire prenup, or specific parts of it, to become void after a certain number of years or after a particular life event.
A 10-year sunset is one of the common ones. Couples who include it are saying that after a decade together, the marriage has proven stable enough that the prenup’s protections are no longer necessary. When the clause takes effect, asset division and spousal support revert to standard state law, as if no agreement ever existed.
Sunset clauses can also be targeted rather than total. A couple might agree that a spousal support waiver expires after 15 years while provisions protecting premarital property stay in place indefinitely. Another common trigger is the birth of the couple’s first child. Courts enforce these provisions like any other contract term.
If you signed a prenup years ago and are not sure what it does at the 10-year mark, pull out the document and read the whole thing. This is the single most common reason an older prenup suddenly stops applying, and it catches people off guard because they forgot what they agreed to back when divorce felt theoretical.
How a Long Marriage Erodes a Prenup Through Commingling
Even when a prenup remains technically valid, the way a couple manages money during a long marriage can quietly gut its protections. This is where 10-year-old prenups most often run into trouble, and it has nothing to do with the paperwork.
A prenup typically classifies certain assets as “separate property” belonging to one spouse. If that spouse deposits separate funds into a joint account, uses marital income to improve a premarital property, or re-titles a separate asset in both names, the line between separate and marital property blurs. Courts call this commingling. Once it happens, the burden shifts to the spouse claiming the asset is separate to trace the money back to its premarital origin. After 10 or 15 years of shared accounts and mixed deposits, that tracing becomes nearly impossible.
Appreciation of premarital assets raises the same problem in a different form. If you owned a rental property before marriage and it rose in value purely because of the market, that growth typically stays separate. But if your spouse spent years managing the property, funding renovations with marital money, or handling tenants, the share of the increase attributable to those marital contributions can become marital property regardless of what the prenup says. The longer the marriage, the more opportunities separate property has to absorb marital effort and dollars.
Couples who want their prenup to retain its force after a decade have to live by it: keep individual accounts for premarital assets, document the source of funds used for any improvements, and think carefully before adding a spouse’s name to premarital property.
Challenging an Older Prenup for Unfairness
A spouse who wants to throw out a prenup without a sunset clause faces a hard climb, but time does create openings that did not exist at the signing. The main argument is unconscionability — the idea that enforcing the agreement would produce a result so one-sided no reasonable person would have accepted it with full information.
Unfair When Signed
Some courts look only at whether the agreement was unfair at the moment it was signed. If one spouse had far more bargaining power, failed to disclose a major asset, or the terms were so lopsided they suggest overreach, a court can refuse to enforce the prenup. Under the Uniform Premarital and Marital Agreements Act, unconscionability is decided by the court as a matter of law, not by a jury.3Uniform Law Commission. Uniform Premarital and Marital Agreements Act
The Second-Look Doctrine
Other states take what family lawyers call a “second look” when the couple actually divorces. Even if the prenup was fair when signed, these states ask whether enforcing it now would be unconscionable given everything that has changed. The Uniform Premarital and Marital Agreements Act contains an optional provision allowing courts to refuse enforcement when it “would result in undue hardship for a party because of a substantial change in circumstances arising since the agreement was signed.”3Uniform Law Commission. Uniform Premarital and Marital Agreements Act
The second-look approach is where time creates the real legal risk for an older prenup. A 25-year-old couple who signed a spousal support waiver when both had entry-level jobs looks very different at 45 if one spouse left the workforce for 15 years to raise children while the other built a high-income career. That is exactly the kind of substantial change that can make a prenup unenforceable under this standard. An agreement a court might leave alone after three years of marriage becomes far more vulnerable after 10 or 20.
The Public Assistance Safety Valve
Even in states that do not follow the full second-look approach, courts keep a narrow override for spousal support. If enforcing a support waiver in the prenup would leave one spouse eligible for public assistance, the court can require the other spouse to provide enough support to prevent that outcome.3Uniform Law Commission. Uniform Premarital and Marital Agreements Act Courts will not enforce a private agreement that shifts the cost of supporting a spouse onto taxpayers.
What No Prenup Can Control, No Matter How Old
Some subjects sit outside what a prenup can decide, regardless of how carefully it was drafted or how long the marriage has lasted. A clause attempting any of these is unenforceable on that point:
- Child support cannot be waived or capped in a prenup. Courts set child support based on the child’s needs and the parents’ income at the time of divorce.4Cornell Law – Legal Information Institute. Uniform Premarital Agreement Act
- Child custody is decided on the child’s best interests at the time of separation. A prenup cannot lock in a custody arrangement years in advance.
- Social Security benefits for a divorced spouse married at least 10 years cannot be waived by any prenup.1Social Security Administration. Benefits Planner – If You Are Divorced
- Survivor annuity rights in a qualified retirement plan are protected by federal law and cannot be waived in a prenup. The right to claim a share of retirement assets as part of property division at divorce is a separate question and can be waived.
What to Do If Your Prenup Is Approaching 10 Years
If the 10-year mark is close, the practical steps are straightforward. First, read the actual document. Check whether it contains a sunset clause, whether that clause is total or partial, and what event or date triggers it. Many people who signed a prenup a decade ago cannot remember the terms, and the answer is usually in the paper itself.
Second, consider whether a postnuptial agreement makes sense. Couples can modify or cancel a prenup at any point during the marriage through a new written contract that amends or replaces the original. The postnup has to follow the same formalities: in writing, signed by both spouses, with fair financial disclosure. An oral promise to ignore the prenup is worthless. Each spouse should have independent legal counsel review any modification, which reduces the risk of a later challenge based on duress or inadequate disclosure.
Third, audit how you have actually been handling money. If separate accounts have become joint, if marital funds have gone into premarital property, or if titles have changed, the prenup may already be weaker than it looks on paper. A review every few years, ideally with an attorney, can catch these drifts before they become permanent and before a divorce forces the question in a courtroom.