A written contract spouses sign after marriage to set rules about money, property, and debt.

"Written" matters because informal promises usually do not hold up when a marriage is under strain. "After marriage" separates it from a prenuptial agreement. "Contract" means both spouses are expected to agree knowingly, voluntarily, and with enough financial disclosure to make the deal fair. And "rules about money, property, and debt" can include who keeps a home, how bank accounts are treated, whether a business stays separate, and who is responsible for certain obligations if there is a divorce, legal separation, or death.

This can become urgent fast when finances change overnight. A serious injury, a new inheritance, a failing business, or a sudden pile of medical bills can turn a manageable marriage issue into a legal emergency. If one spouse is hurt in a crash and later receives an insurance payout or personal injury settlement, a postnuptial agreement may affect whether that recovery is treated as separate property, marital property, or partly both.

In Hawaii, these agreements are not automatic just because both people signed. A family court may look closely at voluntariness, fairness, and full financial disclosure before enforcing one. That matters in a no-fault auto insurance state with mandatory PIP coverage, where injury-related payments, lost wages, and debts can blur together quickly if a couple waits too long to put clear terms in writing.