Cohabitation agreement in Ontario — what it does and when to sign

TL;DR. A cohabitation agreement is a written contract two people sign before or during a common-law relationship that decides — in advance — what happens to property, support, and debt if the relationship ends. In Ontario, common-law partners do not automatically share property the way married spouses do, and the matrimonial-home rules do not apply, but spousal support can still kick in after three years of cohabitation or sooner if there is a child of the relationship. A cohabitation agreement is how you lock down those defaults before things go sideways — and it's the single cheapest legal move a man can make if he owns the house, owns a business, or had a previous separation.

If you are moving in with your girlfriend and you own the condo, the question is not whether you need a cohabitation agreement. It is whether you sign one now or have a much harder conversation in three years.

What is a cohabitation agreement in Ontario?

A cohabitation agreement is a "domestic contract" under section 53 of the Family Law Act. It is a private, binding contract between two people who are living together or about to live together in a conjugal relationship — common-law partners, fiancés, or anyone the Family Law Act would classify as "spouses" by virtue of living together. (Get married after signing one and the cohabitation agreement automatically becomes a marriage contract — section 53(2). No re-signing needed.)

Inside the agreement you can settle anything the two of you want to settle: how property gets divided if the relationship ends, whether spousal support is owed and how much, what happens to the house, how debts get shared, RRSP contributions, life-insurance obligations, who pays for what during the relationship, and how disputes get resolved. The only things you cannot bind in advance are decisions about the children — parenting, decision-making, and child support are always determined at the time of separation based on the children's best interests, no matter what the agreement says.

A cohabitation agreement is the common-law equivalent of a prenuptial agreement. It works the same way, sits under the same section of the Family Law Act, and gets attacked or upheld on the same grounds.

Do common-law partners in Ontario have the same rights as married couples?

No, and this is the part most men have backwards. Ontario law treats married spouses and common-law partners differently on property, the same on support, and similarly on parenting.

Property — different. Married spouses share an "equalization of net family property" — half of what the marriage built. Common-law partners do not. If you cohabit for ten years and own the house alone, your common-law partner has no automatic claim to a share. She would have to sue under a "constructive trust" doctrine and prove she contributed (money or labour) to the asset, and that it would be unjust for you to keep the whole thing — see Ontario's overview of dividing property when a marriage or common-law relationship ends. It is a real claim and it succeeds often, but it is not automatic, and the agreement can shut it down in advance.

Matrimonial home — different. The matrimonial home rules in Part II of the Family Law Act only apply to married couples. Common-law partners have no automatic right to stay in the home, no requirement of joint consent to sell it, and no special status for a home that one partner owned before the relationship. If you own the condo in your name and she moves in, it is still your condo — see your rights to the matrimonial home in Ontario for the married-couple version and how it differs.

Spousal support — same. This is what surprises men most. After three years of continuous cohabitation, or sooner if you and your partner have a child together, common-law partners can claim spousal support against each other under section 29 of the Family Law Act. The amount is calculated using the Spousal Support Advisory Guidelines just like for married couples — see spousal support in Ontario. The difference is only in property; on support, common-law is functionally the same as married.

Parenting and child support — same. Always. Always tied to the child, not to the parents' relationship status. The Federal Child Support Tables apply identically whether you were married or common-law.

So the function of a cohabitation agreement is mostly to: (1) pre-empt the constructive-trust property claim, (2) decide spousal support in advance, and (3) protect specific high-value assets — a business, a pre-relationship home, an inheritance.

What goes in a cohabitation agreement?

The good ones cover seven things:

1. Property brought into the relationship. A schedule listing what each of you owned at the date you moved in — house, RRSPs, business, pension, vehicles, savings. With current values. Updated periodically.

2. Property built during the relationship. How jointly accumulated assets get divided if the relationship ends. Some agreements use a date-of-cohabitation-style equalization (mirroring how a marriage would work). Others keep things separate — "what's in my name stays mine, what's in joint name gets split."

3. The home. Who owns it. What happens if the non-owner contributes to mortgage payments, renovations, or property tax. Whether contribution earns a share. This is the constructive-trust claim, addressed in advance — the agreement can name a fixed buy-out amount, a percentage, or a full release.

4. Spousal support. Whether either of you owes spousal support if the relationship ends. The agreement can name an amount and a duration. It can release support entirely — but a release is the most contestable clause in the agreement, and courts have set them aside under section 33(4) when leaving the support waiver intact would be "unconscionable" at the time of separation.

5. Debts. Joint credit cards, joint lines of credit, joint car loans, jointly co-signed student loans. Who pays during the relationship, how the balance gets allocated if it ends.

6. Death of one partner. What the surviving partner gets from the estate. Without the agreement, Ontario's intestacy rules give a common-law partner nothing by default — she would have to sue under the Succession Law Reform Act dependant's relief provisions to get any share. The agreement can override that with named provisions, life-insurance designations, and estate planning that matches.

7. Dispute resolution. A mediation-first clause. Arbitration if mediation fails. Court as the last step. Includes a clause requiring each party to exchange financial statements if either invokes the dispute mechanism.

Optional but smart: a clause requiring an updated property schedule every three years, and a clause requiring re-execution after any major change (birth of a child, marriage, business sale, inheritance).

Are cohabitation agreements enforceable in Ontario?

Yes — if they were drafted properly. Section 56(4) of the Family Law Act lets a court set aside a domestic contract on three grounds: failure to disclose a significant asset or debt, the affected party not understanding the nature or consequences of the contract, or "otherwise in accordance with the law of contract." Translation: the agreement gets set aside if one of you hid something, did not understand what you were signing, signed under duress, or signed without independent legal advice.

The agreement that holds up has these features:

• Both sides exchanged full sworn financial disclosure — assets, debts, income — before signing. Attached as a schedule.
• Both sides had independent legal advice from their own family lawyer. Each lawyer signs a certificate of ILA at the back of the agreement.
• The agreement was signed and witnessed — written, not oral. Ontario does not enforce oral cohabitation agreements.
• The terms were not unconscionable at the time of signing. A clause that gives one party 100% of the assets and the other party nothing is the kind of clause that gets set aside.
• The agreement was signed without duress — not the night before the wedding, not while one party was in crisis, not when one party did not have time to take it to a lawyer.

The most common reason a cohabitation agreement falls apart in court is incomplete disclosure. If you had a $400,000 LIRA at the date of cohabitation and the schedule does not list it, the court will set the agreement aside fifteen years later — and you will be litigating equalization with a 15-year compounded disadvantage. The agreement is only as strong as the disclosure it was built on.

For a plain-language walkthrough of how the Family Law Act treats common-law relationships, Steps to Justice covers marriage and common-law relationships in Ontario.

When should you sign one?

Three trigger points are worth signing for, in order of urgency:

Before you move in together, if you own the home. This is the cleanest moment to sign. You have time to get to a lawyer. You have time to do disclosure. There is no relationship friction yet. The cost of an Ontario cohabitation agreement at this stage is usually $1,500–$3,500 per side — under $7,000 total, all in.

Before you hit three years of cohabitation, if you did not sign before moving in. Three years is when spousal support attaches automatically under section 29 of the Family Law Act. Sign before that anniversary and you can still settle support in advance. After it, you can still sign — but the negotiating position has shifted.

Before a major asset change. Inheritance, business sale, RRSP rollover, the purchase of a second property. Any moment where one of you is about to acquire or dispose of a significant asset is a moment to update or sign the agreement.

If you are reading this and you are already five years into common-law cohabitation without one, do not assume the moment has passed — a post-cohabitation domestic contract is still possible and still binding, it just has to be drafted with extra care around the disclosure piece. And if the relationship is in trouble already, what you actually need is a separation agreement, not a cohabitation agreement.

The one thing to do this week

Make a one-page list: every asset you own, every debt you owe, every monthly income source, every account number. Today's snapshot. Whether or not you sign anything, the snapshot is the document that protects you — it is the proof of what you brought in, on the date you brought it in. Without it, none of the steps above can protect you.

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