A sunset clause prenup Ontario provision causes a marriage contract to expire automatically after a set number of years of marriage (commonly 10, 15, 20, or 25 years) or upon a specific event. Under Ontario's Family Law Act, R.S.O. 1990, c. F.3, marriage contracts are valid indefinitely unless a sunset clause sets an expiration. Drafting precision is critical: a 2026 lawyer-prepared agreement costs $1,500 to $10,000.
This guide explains how prenup expiration works in Ontario, the legal requirements for enforceability, the drafting risks that void agreements, and how time limit prenup provisions interact with the province's equalization regime. Author: Antonio G. Jimenez, Esq. (Florida Bar No. 21022, covering Ontario divorce law).
Key Facts: Sunset Clause Prenups in Ontario
| Factor | Detail |
|---|---|
| Legal name | Marriage contract (Family Law Act s. 52) |
| Sunset clause cost | $1,500–$10,000 for lawyer-drafted agreement (2026) |
| Default duration | Indefinite (until divorce or death) unless sunset clause added |
| Common expiration points | 10, 15, 20, or 25 years of marriage |
| Formal requirements | Written, signed, witnessed (s. 55) |
| Property division type | Equalization of net family property (Part I, FLA) |
| Divorce residency | 1 year ordinarily resident (Divorce Act s. 3) |
| Divorce court fee | $214 application + $445 hearing list + $10 federal = $669 |
What Is a Sunset Clause in an Ontario Prenup?
A sunset clause is a provision in an Ontario marriage contract that sets an automatic expiration date, after which the agreement becomes null and void. Without a sunset clause, an Ontario marriage contract under Ont. Family Law Act § 52 remains enforceable indefinitely — from signing until divorce or the death of a spouse. A sunset clause changes that default by tying the agreement's validity to the passage of time or a triggering event.
In Ontario, what people commonly call a "prenup" is legally a marriage contract under Ont. Family Law Act § 52. Section 52(1) permits two persons who are married or intend to marry to agree on their respective rights and obligations during marriage and on separation, annulment, dissolution, or death. A sunset clause is one optional term couples may insert. Because a marriage contract is interpreted under ordinary principles of contract law, the exact wording of a sunset clause determines when — and whether — it terminates. Vague drafting is the single most common reason these clauses produce unintended outcomes during a contested divorce.
How Sunset Clauses Work: Three Types
Sunset clauses in Ontario marriage contracts fall into three structures: time-based expiration after a fixed number of years (typically 10, 15, 20, or 25), event-based expiration triggered by a specific occurrence, and phase-out provisions that gradually reduce the agreement's effect over time. Each type carries distinct drafting and enforceability considerations under Ont. Family Law Act § 52.
Time-based expiration is the most common form of prenup duration limit. The agreement automatically voids on a milestone anniversary — for example, "this agreement terminates on the 15th anniversary of the parties' marriage." Event-based expiration ties termination to a defined event, such as the birth of a child or the purchase of a jointly held matrimonial home. Phase-out provisions reduce protection incrementally; a contract might preserve 100% of separate-property protection in years one through five, then step down by a fixed percentage each subsequent year until the agreement dissolves. Couples choose the structure that reflects their evolving financial relationship. The wealthier spouse may prefer a longer prenup expiration window, while the less-wealthy spouse may negotiate a shorter time limit prenup so that protection lapses once the marriage proves durable.
Why Couples Add Sunset Clauses
Couples add sunset clauses to balance asset protection against the long-term commitment of marriage, most often when one spouse holds significantly more wealth. Sunset clauses appear more frequently in marriages with an asset imbalance, allowing the wealthier party a defined "trial" period while giving the less-wealthy spouse assurance that the prenup years married threshold will eventually release them from its terms.
For the wealthier spouse, a sunset clause addresses the fear of a marriage entered for financial security rather than commitment. By setting expiration at, say, 20 years, that spouse limits exposure during the period of highest perceived risk. For the less-wealthy spouse, the same clause offers consolation: after the agreed number of prenup years married, the default equalization regime under Ont. Family Law Act § 52 resumes, restoring a presumptive equal sharing of net family property growth. Sunset clauses also reflect a practical reality — financial circumstances change. A business that was a startup at the wedding may be worth millions two decades later, and a couple may agree that long-married spouses should share that growth. Even where no automatic expiration exists, Ontario family lawyers recommend reviewing a marriage contract every three to five years or after major life events.
Drafting Precision: Why Exact Wording Decides Enforceability
The enforceability of a sunset clause depends entirely on precise drafting, because courts interpret marriage contracts under ordinary contract law. A clause that voids the agreement "upon the seventh anniversary of the marriage" will trigger on that anniversary even if one spouse has already moved out and filed for divorce — because the couple remains legally married until the divorce is granted.
A widely cited illustration involves a couple whose contract stated the agreement "shall become null and void upon the seventh anniversary of the parties' marriage." Four months before that anniversary, one spouse moved out and commenced divorce proceedings. Because divorce litigation takes time, the couple was still legally married on the seventh anniversary — so the clause triggered exactly as written, voiding the prenup and sending property division back to default law. A court noted the result would have differed had the clause voided the agreement "upon the commencement of divorce proceedings" rather than on a calendar anniversary. While this example arose under U.S. law, the governing principle applies in Ontario: a sunset clause is enforceable when its language is unambiguous, and the triggering event must be defined with care. Ontario drafters should specify whether the trigger is the anniversary date, the date of separation, or the date a divorce application is filed under Ont. Family Law Act § 52.
Legal Requirements for a Valid Ontario Marriage Contract
An Ontario marriage contract — with or without a sunset clause — must be in writing, signed by both parties, and witnessed under Ont. Family Law Act § 55. It must also be entered voluntarily, supported by full financial disclosure, and free of unconscionability. Independent legal advice (ILA) for each spouse, while not strictly mandatory, is strongly recommended and often decisive in enforcement disputes.
Section 55(1) imposes the formal requirements: the agreement must be in writing, signed by the parties, and witnessed. Beyond formalities, courts assess substance. Both spouses must sign voluntarily, without duress or undue influence. Each must provide full and frank financial disclosure of assets, debts, and their values — the cornerstone of enforceability under Ontario law. In LeVan v. LeVan (2008 ONCA 388), the Ontario Court of Appeal confirmed that meaningful disclosure is essential for informed consent, and in Dochuk v. Dochuk (1999 CanLII 14971), the court held that even an innocent, non-deceptive failure to disclose can breach the statutory obligation. A marriage contract need not be equal or "fair" in outcome, but it cannot be so lopsided that it shocks the conscience. ILA strengthens enforceability by demonstrating each spouse understood the nature and consequences of the contract under Ont. Family Law Act § 56.
When an Ontario Court Can Set Aside a Sunset Clause Prenup
An Ontario court may set aside a marriage contract — including one with a sunset clause — under Ont. Family Law Act § 56(4) in three circumstances: failure to disclose significant assets or debts existing when the contract was made, a party's failure to understand the contract's nature or consequences, or grounds otherwise available under the law of contract.
Section 56(4) gives courts broad discretion to overturn agreements that fail these tests. The first ground — non-disclosure — is the most litigated. If a spouse concealed a business interest, an inheritance, or a debt when signing, the entire agreement (including its sunset provision) is vulnerable. The second ground addresses comprehension: if a spouse did not understand what rights they were surrendering, perhaps because they signed under time pressure days before the wedding or without ILA, a court may intervene. The third ground imports general contract doctrines — duress, undue influence, unconscionability, and misrepresentation. A sunset clause does not insulate a contract from this scrutiny; it is simply one term within an agreement that must survive Ont. Family Law Act § 56(4) as a whole. Spouses contemplating a time limit prenup should document disclosure and ILA carefully to protect the agreement from later challenge.
What a Sunset Clause Prenup Cannot Override in Ontario
No Ontario marriage contract — regardless of any sunset clause — can validly waive matrimonial home rights, parenting arrangements, decision-making responsibility, parenting time, or child support. Under Ont. Family Law Act § 52(2), a provision limiting a spouse's rights to the matrimonial home is unenforceable, and child-related terms are governed by the best interests of the child at the time of separation.
These limits override private agreement. Section 52(2) renders unenforceable any clause purporting to limit a spouse's right to possession of the matrimonial home under Part II of the FLA — both spouses retain an equal right to remain in the home until a court order or separation agreement says otherwise, even if title is in one spouse's name. A marriage contract may, however, address how the home's value is divided on separation or death. On parenting issues, Ont. Family Law Act § 56(1) bars a marriage contract from governing parenting arrangements (decision-making responsibility and parenting time), because courts always retain jurisdiction to decide a child's best interests under the 2021 Divorce Act amendments. Section 56(1.1) prohibits contracting out of child support, which is the right of the child, not the parent. A sunset clause cannot revive or override these statutory protections.
How Sunset Clauses Interact With Equalization of Net Family Property
When a sunset clause expires, Ontario's default equalization of net family property regime under Part I of the Family Law Act resumes, presumptively dividing the growth in each spouse's net worth during the marriage equally. Before expiration, the marriage contract's terms govern; after expiration, the spouse with greater asset growth may owe an equalization payment representing 50% of the difference.
Equalization is Ontario's core property-division mechanism under Ont. Family Law Act § 52. On separation, each spouse calculates net family property — the increase in net worth from the marriage date to the valuation date — and the spouse with the larger increase pays the other one-half of the difference. A marriage contract commonly opts out of or modifies this regime, protecting business interests, inheritances, or pre-marital assets. A sunset clause sets a deadline on that protection. If a couple's contract expires on the 20th anniversary and they separate in year 22, equalization applies to the full marriage as though no contract existed — the protected assets re-enter the calculation. Couples must understand this consequence: a time limit prenup is not a partial shield that lingers; once it sunsets, the default 50/50 sharing of marital wealth growth applies in full unless a new agreement is executed.
Cost and Process of Adding a Sunset Clause in 2026
A lawyer-drafted Ontario marriage contract with a sunset clause costs between $1,500 and $10,000 in 2026, depending on complexity, asset value, and negotiation. The sunset clause itself adds little marginal cost; the expense lies in financial disclosure, drafting, and independent legal advice for both spouses. Each spouse typically retains a separate lawyer for ILA.
The process begins with full financial disclosure — exchanging sworn statements of assets, debts, and income. Each spouse then obtains independent legal advice, ideally from separate counsel, so neither can later claim they did not understand the agreement under Ont. Family Law Act § 56. The lawyers negotiate terms, including the sunset clause's trigger (anniversary date, separation, or divorce filing) and any phase-out schedule. The agreement is signed and witnessed per Ont. Family Law Act § 55. Unlike a divorce, a marriage contract is not filed with any court and incurs no government filing fee — it is a private contract. Government fees arise only if the marriage later ends in divorce: the Ontario Superior Court of Justice charges $214 to file the application and $445 to place it on the hearing list, plus a $10 federal Central Registry fee, totaling $669. As of April 2026, verify all fees with your local Superior Court of Justice, as amounts are indexed every three years on January 1.