A prenup is only as strong as the process behind it. In Canada, courts have set aside marriage contracts for everything from incomplete financial disclosure to last-minute signing pressure. A flawed prenup isn’t just useless — it can create a false sense of security that makes the eventual separation even more painful and expensive.
If your agreement triggers any of these red flags, it could be worthless when you need it most. For additional common errors, also read Top 5 Mistakes Couples Make With Prenups.
1. You Signed It the Night Before the Wedding
Timing matters — a lot. Canadian courts look at whether both parties had reasonable time to review, consider, and seek legal advice before signing. A contract signed days (or hours) before the ceremony raises serious concerns about duress and undue pressure.
While there’s no statutory minimum timeline in Ontario, most family lawyers recommend finalizing your agreement at least 30 days before the wedding. Some advise 60 to 90 days. The more time between signing and the ceremony, the harder it is for either party to later claim they felt coerced.
For a recommended timeline that builds the prenup into your wedding planning process, see Wedding Planning Checklist: Where Does the Prenup Fit In?.
2. One Partner Didn’t Get Independent Legal Advice
In Ontario, independent legal advice (ILA) isn’t technically required for a marriage contract to be valid under the Family Law Act. But here’s the reality: a court is far more likely to set aside an agreement if one party didn’t have a lawyer review it independently.
ILA protects both sides. It ensures each person understands what they’re agreeing to, what they’re giving up, and whether the terms are reasonable. Skipping this step is one of the most common reasons prenups get challenged — and one of the easiest problems to prevent. Even a single consultation with a family lawyer can dramatically strengthen your agreement’s enforceability.
3. You Didn’t Fully Disclose Your Finances
Full financial disclosure isn’t optional — it’s foundational. If one partner hides assets, understates income, or omits debts, the entire agreement can be voided. Courts take non-disclosure extremely seriously because a contract can’t be fair if one person didn’t have the full picture.
Both partners need to lay everything on the table: income from all sources, assets (including digital assets and cryptocurrency), debts, business interests, expected inheritances, and pensions. A platform like I Do Prenup builds financial disclosure into the process, so nothing gets overlooked.
4. The Terms Are Wildly Unfair
A marriage contract that leaves one partner destitute while the other walks away with everything is unlikely to survive judicial scrutiny. Ontario courts have the power to set aside provisions they find unconscionable — meaning so one-sided that no reasonable person would agree to them under normal circumstances.
A fair agreement balances protection for both partners. It doesn’t have to be perfectly equal, but it should be reasonable and reflect genuine negotiation. If the terms read like a wish list for one side, it’s a red flag that will almost certainly be challenged.
5. You Used a Generic Template
Downloading a prenup template from a random website and filling in the blanks is risky. Canadian family law is province-specific, and a template built for U.S. law (or even another Canadian province) may include clauses that are unenforceable in Ontario. Worse, it may miss required provisions or use language that courts won’t recognize.
Your marriage contract should be tailored to your specific situation and compliant with the Family Law Act. For an overview of what makes Ontario law unique, read What Is a Prenup in Ontario? Myths vs. Reality.
6. You Tried to Include Child Custody
In Canada, you cannot contract about decision-making responsibility and parenting time in a prenup. Period. Courts make custody decisions based on the best interests of the child at the time of separation — not based on an agreement the parents made years earlier. This isn’t a suggestion; it’s a hard legal boundary.
If your prenup includes custody provisions, those clauses will be struck down, and it could cast doubt on the rest of the agreement. A court may question whether parties who included unenforceable terms truly understood what they were signing.
7. There’s No Proper Execution
Ontario’s Family Law Act requires marriage contracts to be in writing, signed by both parties, and witnessed. A verbal agreement means nothing. An unsigned draft means nothing. Even a fully negotiated contract that’s missing a witness signature could be challenged and set aside.
The execution process is straightforward, but it must be done correctly. Both signatures, a witness, and ideally certificates of independent legal advice create a virtually airtight execution.
The Bottom Line
A prenup is a powerful tool — but only when it’s built properly. The good news is that all of these red flags are avoidable. Start the process early, be transparent with your finances, use a platform that understands Canadian family law, and give both partners the time and space to make an informed decision. For context on how Canadian courts evaluate prenups, see How Canadian Courts Handle Prenups.
I Do Prenup guides you through a legally sound process from start to finish. Start your agreement today.
Frequently Asked Questions
Q: Can a prenup be thrown out in Ontario?
Yes. A court can set aside a marriage contract if it finds duress, non-disclosure, unconscionability, or improper execution. Following best practices dramatically reduces this risk.
Q: Is independent legal advice required for a prenup in Ontario?
It’s not legally mandatory, but it’s strongly recommended. Courts are far more likely to uphold an agreement where both parties received ILA.
Q: How far before the wedding should I sign my prenup?
At least 30 days is recommended; 60–90 days is ideal. See our full wedding planning prenup timeline for details.
Q: What happens if my prenup has an unenforceable clause?
In some cases, the unenforceable clause can be severed and the rest of the agreement upheld. However, problematic clauses can cast doubt on the entire contract.