How Do I Make a Prenuptial Agreement That Holds Up?

What a Prenup Can and Can't Cover

A prenuptial agreement — called a marriage contract in Canada or a premarital agreement in the US — is a contract that sets out how a couple's property, debts, and finances will be handled during the relationship and if it ends. You can decide how property acquired before and during the marriage will be divided, protect a business or an inheritance as separate property, allocate responsibility for debts, and set out what happens to assets on death to coordinate with an estate plan. Couples who are living together but not marrying can achieve the same protection through a cohabitation (domestic) agreement, which follows the same rules.

What a prenup cannot do is pre-determine anything about children. Child support belongs to the child, not the parents, and courts in every Canadian province and every US state will decide it — and custody or parenting arrangements — based on the child's best interests at the time of separation, regardless of what the contract says. Any clause fixing or waiving child support or dictating custody is unenforceable, and including one can cast doubt on the whole agreement. Spousal support can be addressed, but a waiver is the term courts scrutinize most closely.

The Four Pillars of Enforceability

For a prenup to survive a challenge, four things must be true. First, it must be in writing, signed, and (in most jurisdictions) witnessed — an oral agreement is worthless. Second, both parties must exchange full and honest financial disclosure of their assets, debts, and income, usually as sworn schedules attached to the agreement; hidden or understated assets are the most common reason prenups are set aside. Third, each party should have independent legal advice from their own separate lawyer, which demonstrates they understood the agreement and its consequences. Fourth, the agreement must be signed voluntarily, without duress or undue pressure — which is why signing on the eve of the wedding is so dangerous.

The legal framework differs between the two countries. In the US, roughly 28 states have adopted the Uniform Premarital Agreement Act (UPAA) or its successor the Uniform Premarital and Marital Agreements Act (UPMAA), which make premarital agreements presumptively enforceable if these formalities are met — though a court can still refuse to enforce an unconscionable agreement or one signed involuntarily, and some states impose a waiting period between review and signing. In Canada, domestic contracts are governed by provincial family law statutes and the Supreme Court's decisions in Miglin and Hartshorne, under which a court can set aside or override an agreement that was unfairly made or that operates unfairly at the time of separation.

Timing, Business Protection, and Second Marriages

Timing matters more than most couples expect. Beginning the process months before the wedding — not weeks — gives each party time to obtain advice, exchange disclosure, and negotiate without pressure, and it removes the strongest argument against enforceability. Practitioners commonly recommend signing at least 30 days before the wedding, and a handful of US states require a formal waiting or review period. If the wedding is imminent, a postnuptial or marriage contract signed after the wedding is often a safer route than a rushed prenup.

Prenups are especially valuable in two situations. Business owners use them to keep a company, its future growth, and reinvested earnings as separate property, and partners or investors frequently require one as a condition of shareholder or partnership agreements. People entering a second marriage — particularly with children from a prior relationship — use them to protect assets intended for those children and to coordinate with wills and beneficiary designations, preventing future litigation between a surviving spouse and the children. In both cases, careful tracing of pre-owned property and clear rules about commingling are what make the protection actually work.

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