A prenup in Australia does not automatically expire the way a driver's licence or insurance policy does. Once signed and properly executed, a binding financial agreement (BFA) continues to operate unless something causes it to be set aside or terminated. That said, "technically still valid" and "practically enforceable" are two very different things, and understanding the gap between them is important before you rely on an agreement you may have signed years ago.
No automatic expiry, but not invincible
Under the Family Law Act 1975 (Cth), a BFA has no fixed lifespan. It remains on foot until a court sets it aside, the parties terminate it by written agreement, or a specific terminating event named in the agreement itself occurs. This means a prenup signed before a wedding can, in principle, still govern a property dispute decades later. The question is whether it will survive scrutiny at that point.
Courts look carefully at whether the agreement was fair and properly made at the time it was executed. The longer the gap between signing and separation, the greater the chance that circumstances have changed enough to raise genuine questions about the agreement's continued relevance. This is not the same as expiry, but the practical effect can be similar.
Events that can undermine a prenup over time
Several developments can erode the strength of a prenup without formally voiding it. Being aware of these gives you the opportunity to review and, if necessary, update the agreement:
- Significant changes in financial circumstances. If one partner's wealth increases dramatically, or a business grows far beyond what the agreement contemplated, the terms may no longer reflect a just outcome.
- The birth or adoption of children. A prenup executed before children arrived may not address parenting-related financial arrangements, which can affect how a court views the agreement.
- A major shift in the asset pool. Selling properties, acquiring new ones, or inheriting assets can leave gaps in an agreement that was written around a different set of circumstances.
- Flawed legal advice at the time of signing. If either party did not receive independent legal advice before executing the agreement, a court may set it aside regardless of how old or recent it is. This is one of the most common grounds for a BFA being overturned.
- Evidence of duress or unconscionable conduct. Courts can and do set aside agreements that were signed under pressure, even many years after the fact.
What makes a prenup vulnerable at the time of enforcement
When a relationship ends and one party seeks to rely on a prenup, the other party may challenge it. The grounds that determine whether a binding financial agreement is enforceable are assessed at the point of dispute, not at the point of signing. This is a critical distinction. An agreement that appeared solid when it was made may have weaknesses that only become apparent years later.
Common vulnerabilities include incomplete financial disclosure at the time of signing, clauses that were not properly drafted to cover the assets actually in dispute, and advice that was superficial rather than genuinely independent. A court that finds any of these issues can set the agreement aside, effectively leaving the parties in the same position as if no prenup existed.
Can you update a prenup after marriage or during a de facto relationship?
Yes. Parties can enter into a new financial agreement during a relationship, which can replace or supplement an earlier one. You can also mutually terminate an existing agreement by executing a written termination document that meets the same formal requirements as the original. Both parties need independent legal advice for that termination to be valid.
Reviewing a prenup every few years, or after a major life event such as buying property or having children, is sensible practice. It is far easier to update an agreement proactively than to defend a stale one in court. If you are unsure when a prenup is appropriate and what it should cover, getting legal advice sooner rather than later keeps your options open.
What about de facto couples?
De facto couples in Australia can enter into BFAs that govern property and financial matters both during and after a relationship. The same rules apply: the agreement does not expire automatically, but it can be challenged on the same grounds that apply to married couples. Given that de facto relationships can sometimes end without the formal milestone of a divorce, it is worth ensuring any agreement is clearly drafted to cover the specific nature of the relationship. For more on how separation works for de facto partners, see our article on de facto break up entitlements in Australia.
How to keep a prenup effective over time
The short answer is: review it regularly and update it when circumstances change significantly. Here are some practical steps that can help:
- Schedule a review with your family lawyer every three to five years, or sooner if a major financial or personal event occurs.
- Keep records of the independent legal advice both parties received at the time of signing. This documentation matters if the agreement is ever challenged.
- If the original agreement no longer reflects your actual asset pool or intentions, execute a new one rather than relying on an outdated document.
- Avoid making informal amendments or additions. Any changes need to meet the same formal requirements as the original agreement to be binding.
A prenup that was carefully drafted and has been periodically reviewed is far more likely to hold up when it is needed than one that was signed before the wedding and never looked at again. The investment of time to maintain the agreement properly is modest compared to the cost of litigating a property dispute without one.
Getting the right advice
Because the enforceability of a BFA is assessed at the time of any dispute, the quality of the original legal advice and the continued relevance of the agreement's terms both matter. Family law is an area where the gap between a technically valid document and a practically effective one can be significant. If you have an existing prenup and are unsure whether it would withstand scrutiny, speaking with an experienced family lawyer is the clearest way to find out.