Section 21J and when a court sets an agreement aside
Updated 2026-08-09. General information, not legal advice.
Section 21J of the Property (Relationships) Act 1976 is the safety valve on contracting out. It lets a court set aside a contracting out agreement, even one signed with every formality met, if giving effect to the agreement would cause serious injustice. The bar is deliberately high. Courts start from the position that agreements freely and properly made should stand, and that a bargain merely turning out badly for one partner is not injustice. Serious injustice is reserved for agreements whose enforcement would be plainly wrong in the circumstances as they now exist.
What does a court weigh under section 21J?
The statute directs attention to matters like these: the circumstances in which the agreement was made, including pressure and the quality of disclosure; the length of time since it was made; whether the agreement was unfair or unreasonable when made; whether it has become unfair or unreasonable in light of changes since; the fact that the partners wanted certainty; and anything else the court considers relevant. No single factor decides it; the question is the overall justice of enforcing this agreement between these people now.
What does serious injustice look like in practice?
The recurring patterns: an agreement signed days before a wedding under an effective ultimatum; disclosure that concealed the true asset position; an agreement made for a brief early relationship that then ran decades, produced children and a jointly built business, and was never reviewed; and terms that leave one partner with essentially nothing after years of contribution while the other keeps everything. Contrast the agreement that was fair when made, reviewed as life changed, and still leaves both partners in a defensible position: that agreement holds.
How do you draft against a section 21J challenge?
Treat 21J as a design constraint from day one. Full, documented disclosure. Signing well clear of any deadline. Terms that acknowledge non-financial contributions and do not strip a partner bare. Genuine independent advice on both sides, under section 21F, with time to negotiate. And reviews at major life events, so the agreement never drifts far from the life it governs. An agreement built this way gives a future court every reason to do what courts prefer to do anyway: hold the parties to their bargain.
Common questions
- What is serious injustice under section 21J?
- A high threshold for setting aside a contracting out agreement: enforcing the agreement must be seriously unjust in all the circumstances, weighing how it was made, the time elapsed, fairness then and now, and the parties' wish for certainty. Ordinary unfairness or regret is not enough.
- Does section 21J make prenups pointless?
- No. Courts respect properly made agreements and set aside relatively few. The section polices the extremes, coerced, concealed or badly outdated agreements, and a couple who drafts fairly and reviews periodically is building the very record that defeats a challenge.
- Who has to prove serious injustice?
- The partner asking the court to set the agreement aside. The starting point is that the agreement stands; the challenger must persuade the court that enforcement would cause serious injustice.
- If an agreement is set aside, what happens?
- The Act's default rules apply to the division as if the agreement did not govern it, generally equal sharing of relationship property. The court does not rewrite the agreement into something fairer; it disapplies it.
Sources
All information published on prenup.nz, including this guide, is general information only and is not to be construed as legal advice. We strongly recommend seeking independent legal advice about your own situation. A contracting out agreement only binds you once each partner has taken independent legal advice and a lawyer has witnessed and certified each signature, as section 21F of the Property (Relationships) Act 1976 requires.