Canadians borrowed the word prenup from American television, and it stuck. The paperwork behind it has a duller name, provincial rules, and a short list of things it can never do. Signing one takes an afternoon. Unwinding a badly built one takes years.
Short answer: So what is a prenup? It is an agreement two people sign before marriage that settles property, debts and spousal support during the marriage, on separation and on death. Ontario law calls it a marriage contract under section 52 of the Family Law Act. It has to be in writing, signed and witnessed, and it cannot bind a judge on child support.
Key takeaways
- The legal name is a marriage contract, one type of domestic contract. Lawyers in some provinces still say prenuptial agreement or domestic agreement.
- Property division rules come from your province, not from Ottawa, so a Quebec contract and an Ontario one are built differently.
- Two failures sink more agreements than everything else combined: hiding assets or debts, and one spouse signing without their own lawyer.
- You cannot sign away child support, and in Ontario you cannot decide in advance who gets to stay in the matrimonial home.
- Budget CA$1,500 to CA$3,500 per person for a straightforward agreement, and far more once a business or a trust is in the picture.
What is a prenup under Canadian law?
It is a contract, and a fairly ordinary one. Ontario’s Family Law Act groups it with separation agreements, cohabitation agreements and family arbitration agreements under the umbrella term domestic contract. Section 52 lets two people who are married, or who intend to marry, agree on their rights and obligations. That covers the marriage itself, separation, the end of the marriage and death.
The word prenup is a description of timing, not a legal category. Sign the same document a week after the wedding, and it is still a marriage contract, with identical force. Couples who are not marrying use a cohabitation agreement instead, which in Ontario converts into a marriage contract automatically if they later marry.
Terminology shifts across the country. Alberta and British Columbia lawyers talk about prenuptial agreements or simply agreements under their family property statutes. Quebec sits outside the common law system entirely, and a Quebec marriage contract has to be signed before a notary as a notarial act.
What a marriage contract can and cannot decide
Most disappointment with these agreements comes from a mismatch between what people assume they bought and what the statute allows. Here is the honest split.
| Issue | Can your contract settle it? | The catch |
|---|---|---|
| Who owns what, and how property gets divided | Yes | This is the core purpose. You can opt out of the default sharing formula almost entirely. |
| Debts each of you brought in | Yes, between the two of you | Your lender is not a party. A bank still chases whoever signed the loan. |
| Spousal support, including a waiver | Yes, with real risk | A judge can override a waiver that has become unconscionable by the time you separate. |
| An inheritance or a gift from your parents | Yes | Already partly protected in Ontario, but a clause removes the argument about tracing. |
| A business, professional practice or corporation | Yes | Needs a valuation date and a formula; otherwise, you have written a lawsuit. |
| Child support | No | The money belongs to the child. A waiver clause is worth nothing. |
| Parenting time and decision-making | Not in any binding way | A court applies the best interests of the child at the time, whatever you wrote years earlier. |
| Possession of the matrimonial home in Ontario | No | Section 52 makes any clause limiting those rights unenforceable. |
Child support deserves the plain version. It belongs to the child rather than to the parent who receives it, so a clause promising never to claim it buys the payer no protection at all. According to the Department of Justice Canada, judges set amounts using the Federal Child Support Guidelines, and updated child support tables took effect on October 1, 2025. A judge who reads your agreement can still order the table amount.
If you want the arithmetic behind that number, our explainer on how a Canadian child support amount is built walks through income, table figures and the extras parents share.
The matrimonial home rule that catches Ontario couples
Two separate rules apply to the house, and people routinely confuse them. The first is possession. Both spouses hold an equal right to live in the matrimonial home while the marriage lasts, whatever the title says. A marriage contract cannot take that away. You can agree who owns the house and who gets the value. You cannot agree that one of you will pack a bag on separation day.
The second rule costs more money.
In Ontario, property you owned on the wedding day comes off your net family property as a date of marriage deduction, so you only share the growth. The matrimonial home is the exception. Say you bring a paid-off condo worth CA$600,000 into the marriage and the couple lives in it. That entire CA$600,000 falls into the sharing pot on separation. A well-drafted contract fixes this in a single clause, and couples who skip the contract discover the rule far too late.
The signing rules that make it valid
Formal validity in Ontario is short enough to memorise. The agreement must be in writing. Both spouses must sign it. A witness must sign as well, and that witness signature is the requirement people forget, because nothing about a printed document looks incomplete without it.
Three practical points sit on top of the statute:
- Sign well before the wedding. An agreement produced two days before 120 guests arrive invites an argument about pressure.
- Attach the financial disclosure as sworn schedules rather than describing it loosely in a recital.
- Keep a signed original each, plus the lawyers’ files. Reconstructing a lost agreement fifteen years later is grim work.
The two failures that get agreements set aside
Courts do not tear up marriage contracts because the deal looks harsh. Section 56 of the Family Law Act gives a judge three routes. One spouse failed to disclose significant assets or debts. One spouse did not understand the nature or consequences of what they signed. Or ordinary contract law voids the deal for duress, fraud or undue influence.
The first two routes account for nearly every successful challenge.
Incomplete disclosure. Each spouse has to put their assets, debts and income on the table before signing. A forgotten rental property or a quiet line of credit hands the other side a set-aside argument years later. Sworn schedules are what prove you did it properly.
No independent legal advice. Ontario’s statute does not strictly require each spouse to have their own lawyer, but judges treat its absence as a warning light.
Alberta goes further: under its family property legislation, an agreement is only enforceable if each spouse received independent legal advice and the lawyer certified it. British Columbia gives a court its own list. A judge there can set an agreement aside for non-disclosure. Improper advantage taken of one spouse’s vulnerability counts too, as does an outcome that meets the statutory test of unfairness.
| Province | Usual name | Formality that trips people up |
|---|---|---|
| Ontario | Marriage contract, Family Law Act s. 52 | Written, signed, witnessed; no clause on matrimonial home possession |
| British Columbia | Agreement respecting property | Written and witnessed; set aside where the outcome is significantly unfair |
| Alberta | Prenuptial or property agreement | Independent legal advice with a lawyer’s certificate, or it does not bind |
| Quebec | Marriage contract | Notarial act before a notary; family patrimony cannot be waived in advance |
How it interacts with equalization of net family property
Ontario does not split assets item by item. Each spouse totals what they own on separation day, subtracts debts, then subtracts the value they brought to the marriage. Excluded property also comes out, such as a third-party gift or an inheritance that arrived during the marriage. Whoever ends up with the larger figure pays half the difference to the other. That payment is the equalization payment.
A marriage contract works on this formula rather than replacing it. Typical clauses exclude a business from the calculation, fix an asset’s value as of the wedding day, or replace equalization with an agreed lump sum. Many also handle the matrimonial home deduction. Some couples opt out of the whole scheme and agree that each keeps what stands in their own name.
None of that changes the tax rules, the pension rules or a creditor’s rights. The contract binds you and your spouse, and nobody else.
What happens when a spouse dies
Death is the part almost every online explainer skips. In Ontario, a surviving spouse gets a choice: take what the will leaves them, or make an equalization claim against the estate as if the couple had separated. The election has a six-month deadline from the date of death, and missing it usually means taking the will.
A marriage contract can settle that question in advance, which is exactly why estate lawyers ask to see one. Two cautions. A marriage contract does not rewrite your will. It also leaves beneficiary designations on registered plans and life insurance untouched, so those documents have to match the contract.
Well-drafted agreements often include a promise to keep a specific will or policy in place, and that promise is enforceable against the estate. You will find more on the overlap between estate and family law across our Canadian family law guides.
Changing or cancelling the agreement later
You can do both, and the formality follows the original. An amendment or a full rescission has to be in writing, signed by both spouses and witnessed, exactly like the contract it changes. A verbal promise over dinner changes nothing.
Sensible triggers for a review include a first child, a business sale, a move to another province, an inheritance landing, or one spouse leaving paid work for several years. Provinces treat property differently, so a contract written for Ontario and carried to Quebec deserves a fresh read by a lawyer there.
What does a prenup cost in Canada?
Family lawyers price this work in a fairly narrow band, and most quote a flat fee once they see the assets. These are the ranges couples typically face across Canadian firms in 2026:
- Review and independent legal advice on a draft the other side prepared: CA$750 to CA$2,000.
- Drafting and negotiating a straightforward agreement: CA$1,500 to CA$3,500 per person, so roughly CA$3,000 to CA$7,000 for the couple.
- Complex files with a corporation, a trust, a blended family, or assets in two countries: CA$5,000 to CA$15,000 for the pair, sometimes higher.
- Attacking or defending an agreement in court years later: CA$20,000 to CA$75,000, and that is before the property fight itself.
Rates run higher in Toronto and Vancouver than in smaller centres. The last line is the argument for the first three: the cheapest agreement is the one nobody litigates.
Your next step
Start with a list. Write down what each of you owns, what each of you owes, and the two or three outcomes you want locked down. That list is what a lawyer needs, and it turns a vague worry into an hour of billable work rather than five.
Then get advice on your own province’s rules, because the province decides how your property gets divided. If you want help finding the right starting point, reach out to the Lawverra team, and we will point you toward the right resources. This article is general information for Canadian readers, not legal advice for your situation.
Frequently asked questions
A marriage contract. It is one of the domestic contracts named in the Family Law Act, alongside separation agreements and cohabitation agreements. Lawyers understand prenup perfectly well, but the document itself will use the statutory term.
Yes. A marriage contract signed during the marriage carries the same weight as one signed before it, and the timing changes nothing about the writing, signing and witnessing rules.
In Alberta, yes, because enforceability depends on it. Everywhere else it is technically optional and practically essential. One lawyer cannot advise both of you, and a spouse who signed without advice has the easiest challenge available.
Usually it confirms protection you already have. Ontario excludes a gift or inheritance from a third party received during the marriage, provided you can trace it. Money mixed into a joint account or spent on the family home loses that character, and a contract lets you address the problem before it arises.
On child support and parenting, yes, without hesitation. On property and spousal support, a judge starts from your agreement. Departing from it takes a reason under section 56, such as concealed assets or a spouse who never grasped the deal.
No. Business owners benefit most, along with anyone entering a second marriage with children from the first. So does the spouse who brings a home, or a large debt, into the relationship.
