Ontario Prenup: What a Marriage Contract Can and Cannot Cover

A marriage contract — what most people call a prenup — is one of the most misunderstood documents in family law. Some people think it's a sign of distrust; others assume it can fix any future dispute. The truth is more practical: a well-drafted Ontario marriage contract covers a specific set of issues and is legally barred from addressing others. Knowing the boundaries upfront lets you use this tool the way it was designed.

Ontario's Family Law Act specifically governs marriage contracts. Under that legislation, couples who are married or about to marry can enter into a written agreement dealing with their rights and obligations — but only within the limits the Act sets.

What a Marriage Contract CAN Cover

1. Property Ownership and Division

Marriage contracts can define what property each person owns, how property acquired before or during the marriage will be treated, and how assets will be divided if the marriage ends.

This is often the core purpose. Without a marriage contract, Ontario's equalization of net family property rules apply — meaning the spouse who accumulated more net property during the marriage must pay the other half the difference. A marriage contract can modify or opt out of those default rules.

Common uses include:

• Protecting a family business or professional practice from equalization claims
• Treating an inheritance or gift as excluded from equalization even if it appreciates during the marriage
• Specifying that certain pre-marital assets remain separate
• Agreeing on how jointly-purchased property will be handled on separation

2. Spousal Support

Marriage contracts can address whether either spouse will pay support after separation, in what amount, and for how long. Couples sometimes waive spousal support entirely, or set a formula tied to the length of the marriage.

Important caveat: Courts have the power to disregard a spousal support clause if enforcing it would cause one spouse unconscionable hardship — particularly if circumstances changed dramatically (serious illness, loss of employment, decades-long marriage with one spouse out of the workforce). A blanket waiver signed early in a long marriage carries more risk than one negotiated after both parties fully understand their financial positions.

3. Rights and Obligations During the Marriage

Marriage contracts can deal with how finances are managed during the marriage — separate bank accounts, responsibility for specific debts, how household expenses are shared.

4. Estate and Inheritance Rights

A marriage contract can modify or waive the right to elect against a deceased spouse's will (the equalization on death right under the Family Law Act). This is often relevant in second marriages where each spouse has adult children from a prior relationship.

What a Marriage Contract CANNOT Cover

The Family Law Act places hard limits on what a marriage contract may address. Clauses outside these limits are simply unenforceable — a court will strike them and, in some cases, use their presence to question the agreement's overall fairness.

1. Custody and Access (Decision-Making Responsibility and Parenting Time)

A marriage contract cannot determine decision-making responsibility for children or parenting time (what older law called custody and access). Those decisions belong to the children and the courts, assessed on the best interests of the child at the time of separation — not the intentions of the parents years earlier.

You can include an aspirational dispute-resolution clause (agreeing to try mediation first, for example), but you cannot bind a court to a particular parenting arrangement.

2. Child Support

Marriage contracts cannot waive or limit a child's right to support. Child support in Ontario is governed by the Federal Child Support Guidelines and belongs to the child — not the parents — so parents cannot bargain it away.

3. Possession of the Matrimonial Home During the Marriage

There are strict limits on what a marriage contract can say about who has the right to possess the matrimonial home if the parties are living together. The Family Law Act grants both spouses equal possession rights in a matrimonial home, and contracts that purport to take away that right are void to that extent.

On separation, a marriage contract can address who keeps the home or how its value is divided — that part is enforceable.

4. Directions That Are Contrary to Public Policy

Clauses that, for example, contemplate illegal arrangements, penalize a spouse for seeking legal advice, or attempt to strip a spouse of all economic protection in a wildly disproportionate way, will not be enforced.

Special Considerations: The Matrimonial Home

The matrimonial home sits at the intersection of several rules and deserves its own mention. By default, the value of the matrimonial home receives no deduction for its pre-marital value in the equalization calculation — meaning if you owned your home before you married, you don't get credit for that pre-marital equity. A marriage contract can restore that deduction. This is a common reason people with significant home equity before marriage decide to put a contract in place.

The Process: What Drafting Looks Like

A properly drafted marriage contract typically involves:

1. Financial disclosure — each party prepares a full picture of assets, debts, and income
2. Drafting by one party's lawyer
3. Review by the other party's independent lawyer, who provides independent legal advice
4. Negotiation of any changes
5. Signing before witnesses, with each lawyer certifying their client received independent legal advice

Rushing this process — or springing it just before the wedding — is one of the most reliable ways to end up with an agreement a court will set aside.

Frequently asked questions