This week's Divorce Gotcha: Many Ontario couples live as common-law partners with no legal claim to the home they've been paying into for years. Here's the document that changes that — and why nobody signs it until it's too late.

Eight years. Two kids. A shared mortgage on a house that went from $500,000 to $900,000.

Her name wasn't on the title.

When Sarah and Marcus split up, Marcus kept the house. Not because he was vindictive — he wasn't particularly. Not because she gave up her claim in some dramatic negotiation. He kept it because it was legally his. The mortgage was in his name. The title was in his name. And Ontario law, as it turns out, is brutally literal about these things.

Sarah had contributed to the household for eight years — groceries, utilities, renovation costs, and a portion of the mortgage. She'd taken a lower-paying job to be closer to home and spend more time with the kids. Under Ontario's default rules for common-law partners, none of that created an automatic legal claim to the home. She could argue unjust enrichment in court — an expensive, uncertain litigation fight with no guaranteed outcome — or she could walk away.

She walked away.

The document that could have changed this entire outcome is a cohabitation agreement. A contract that would have taken a few hours to negotiate and cost each of them a few hundred dollars in legal fees. Signed before they moved in together, it would have spelled out exactly what ownership interest she'd accumulate over time. It would have turned a costly, murky dispute into a resolved contract.

They didn't sign one. Most common-law couples in Ontario don't. The reason is always the same: nobody thinks they'll need it.

Here's what a cohabitation agreement actually does in Ontario, what it can and can't protect, and the timing gotcha that makes this document completely useless if you wait too long.

Before getting into what a cohabitation agreement does, it's worth being clear about what common-law partners actually get in Ontario without one. A lot of people have this wrong—some think they're fully protected, others think they have no rights at all. The truth is more specific than either.

Once you qualify as common-law—either through 3 years of cohabitation, or any time if you have a child together—you have the same spousal support rights and obligations as married couples. The Spousal Support Advisory Guidelines (SSAG) apply. The Rule of 65 applies. The formulas that determine how much support is owed and for how long work exactly the same as for married couples.

You also have child support rights—same Child Support Guidelines as married couples, with no minimum cohabitation period required. And if you've lived together for at least 12 consecutive months and then been separated for at least 12 consecutive months, either of you can apply to split CPP credits that accumulated during the relationship.

The big one: no automatic property rights.

Ontario's net family property rules create an automatic roughly 50/50 division of assets accumulated during a marriage. Common-law couples have none of that. The general principle is: when you separate, you take what's in your own name. Full stop.

A cohabitation agreement is how you address that property column. Without one, common-law couples operate under the default rules — which often produce outcomes neither partner expected or intended.

Under Ontario's default rules, common-law partners keep what's in their own name when they separate. If you bought a home together and both names are on title, you each own 50%. If only one name is on the title, that person owns the home.

There's a legal claim called unjust enrichment that lets a partner argue they contributed to an asset that's in the other's name, and that it would be unfair for the registered owner to keep all of it. To succeed, you have to prove three things:

Courts have recognized that non-financial contributions matter. Often in long relationships, one partner spends more time maintaining the household and raising children, which allows the other to dedicate more time to their career and accumulate assets. Courts have stated that in situations like these, consideration should be given to those non-financial contributions.

But here's the reality: unjust enrichment claims are expensive, uncertain, and time-consuming. They require litigation. Even when they succeed, the split isn't necessarily 50/50. A cohabitation agreement settles all of this upfront, before there's a dispute.

A cohabitation agreement can address almost anything the couple agrees to. Common provisions include:

The most important section for most couples. You can specify exactly how property acquired during the relationship will be divided — whether that's 50/50, proportional to each partner's financial contribution, or some other arrangement the couple agrees to. You can also address how jointly acquired land will be handled, including whether one partner can buy out the other or whether the property must be sold.

If one partner owns a home, investments, or other assets before moving in together, the agreement can document what each person brought in — and confirm that those pre-relationship assets remain separate. This is especially important for someone who already owns a home. Without clear documentation, disputes can arise later about whether contributions during the relationship gave the other partner a claim to those pre-existing assets.

You can limit or waive spousal support in a cohabitation agreement. Some couples agree that neither will claim support from the other; others set a cap on the amount or duration. This is particularly useful when both partners earn similar incomes and the risk of a significant future income gap seems low.

Be aware: a spousal support waiver is not guaranteed to hold. Courts can override it if enforcing the waiver would leave one partner in serious financial need, or if circumstances have changed dramatically since the agreement was signed. A clause written when both partners were earning similar salaries may not hold if one partner later left the workforce to raise children. More on this below.

Some couples want to spell out how shared expenses are handled — who pays what, whether rent paid to a partner who owns the home creates any ownership interest, how household contributions are tracked. These provisions prevent ambiguity about whether contributions during the relationship create property claims later.

Which debts each partner brings into the relationship stay with that partner. What happens to debts incurred during the relationship. A cohabitation agreement can specify which partner is responsible for what — so there's no dispute about joint exposure when things end.

The situation: Marcus owns a condo worth $600,000 when he and Priya move in together. Over 7 years, Priya contributes to household expenses, renovation costs, and the mortgage. Marcus's name is the only name on the title.

Without a cohabitation agreement: Priya has no automatic claim to the condo. She may have an unjust enrichment argument based on her financial and non-financial contributions, but she's looking at expensive, uncertain litigation with no guaranteed outcome.

With a cohabitation agreement: The agreement — signed before they moved in — specified how Priya's contributions would be treated and what ownership interest she would accumulate over time. The dispute is resolved by the contract, not the courts.

Either way: Spousal support is a separate question entirely. If they've lived together 3+ years, Priya may qualify for spousal support based on the income difference and length of the relationship — regardless of what the property agreement says.

There are real limits to what you can contract away.

You cannot waive or limit child support in a cohabitation agreement. Child support is the child's legal right, not the parents'. Parents cannot contract it away between themselves. If you have children together, child support will be determined by the Child Support Guidelines regardless of what your cohabitation agreement says.

A cohabitation agreement can include a spousal support waiver, but courts can override it if:

This doesn't make a spousal support waiver useless. A well-drafted one, signed with proper independent legal advice when both parties were on equal footing, carries real weight. The point is don't assume it's bulletproof — especially if circumstances shift significantly during a long relationship.

Courts won't enforce terms that are grossly unfair. An agreement signed under duress, without understanding what was being agreed to, or in circumstances where one party exploited the other's vulnerability — that agreement is at risk of being set aside, regardless of the specific language. The process that produced the agreement matters as much as what the agreement says.

A cohabitation agreement is only as strong as the process that created it. Three things determine whether yours will survive a challenge:

Cohabitation agreements must be skillfully drafted to actually say what you intend. Vague language, missing provisions, or clauses that contradict each other create exactly the ambiguity you were trying to avoid. A sentence that seems clear when you write it can be argued two different ways in a courtroom years later.

Family lawyers who regularly work with domestic contracts know the provisions couples commonly miss. A clause that seems minor when you draft the agreement can become the most important sentence in the document when you separate.

Full financial disclosure is the most common reason family law agreements get set aside. The point is that both partners can only make an informed decision about what they're agreeing to if they have an accurate picture of each other's finances. If one partner hides assets, understates income, or provides misleading information, the other partner didn't actually get to make an informed choice.

If the agreement is later challenged and it comes out that one party failed to disclose fully, a court can set the entire agreement aside — not just the provision that was affected by the missing information. The disclosure failure undermines the whole contract.

Independent legal advice (ILA) means each of you has your own separate lawyer — not one shared lawyer, not the same person advising both sides — review the agreement and explain what you're agreeing to before you sign. One of the major factors courts consider when deciding whether to uphold a family law agreement is whether both parties were educated about their rights and obligations, and whether they received ILA prior to signing.

An agreement signed without ILA isn't automatically void. But it's significantly more vulnerable to being set aside. The partner who didn't get independent advice can argue they didn't understand what they were agreeing to — and courts take that seriously.

Even if you draft the agreement yourselves, each of you should have a separate lawyer review it before you sign. The cost of that review is far lower than the cost of having the agreement thrown out — or fighting a property dispute through the courts without one.

Here's the thing that doesn't get said clearly enough: a cohabitation agreement is a before-the-fact document. The time to get one is before you move in together, or early in the relationship. Not when things are going badly. Not after years of shared property and complicated financial history. Definitely not after you've already separated.

Negotiations are much easier before the relationship deepens financially. Both partners are on more equal footing. Neither has contributed years of their life and career to the other's benefit. The financial picture is simpler. The power dynamics are cleaner.

Mid-relationship agreements are possible — and better than nothing — but they're more complicated. Both partners know a lot more about the financial situation at that point, which makes negotiations more contentious. Courts also scrutinize these agreements more carefully, since financial imbalances between partners are already established by the time they sign.

Both parties should receive independent legal advice before signing. That doesn't necessarily mean hiring a lawyer to manage the entire process from start to finish.

Many Ontario family lawyers offer limited scope retainers or unbundled services — where they help with a specific part of the process rather than the whole matter. For a cohabitation agreement, a limited scope retainer might include:

Not every lawyer offers unbundled services, but many do. It's worth asking. The cost of an ILA review is significantly lower than the cost of having a court set the agreement aside — or fighting an unjust enrichment claim through litigation without any agreement in place.

If you're already in a common-law relationship and don't have a cohabitation agreement, a mid-relationship agreement is still an option. It's more complicated than signing one before you move in, but better than no agreement at all.

A few things to keep in mind:

It's also worth thinking practically about what you're trying to accomplish. If your main concern is the home — who owns what if you separate — the most straightforward solution may be to put both names on title, rather than trying to establish ownership interests through a contract alone.

Property division and spousal support are separate issues. A cohabitation agreement can address both — but what happens to property doesn't automatically determine what happens with support. They operate independently.

If you've lived together for 3 years or have a child together, you may qualify for spousal support regardless of any property agreement. Spousal support is calculated based on income difference, length of the relationship, and other factors — not who owns the home. A cohabitation agreement can attempt to limit or waive support, but that waiver isn't guaranteed to hold if circumstances have shifted significantly.

For a full explanation of how common-law spousal support works — when it applies, how it's calculated, and what the Rule of 65 means for common-law couples — see our article on common law spousal support in Ontario.

This is not legal advice. Whether a cohabitation agreement is right for your situation depends on the specific facts of your relationship and your financial circumstances. The enforceability of any particular clause depends on how it was drafted, the circumstances at signing, and subsequent changes in your situation. If you're considering a cohabitation agreement, consult with a family lawyer before signing anything.

To find out what you will have to pay for spousal support or what you will be paid, there’s a free spousal support calculator (including a child support calculator and net property calculator) at ontariospousalsupport.com

This article is for general informational purposes only and is not legal advice. Family law outcomes depend on the facts of each case and courts retain discretion when applying the Spousal Support Advisory Guidelines.