Prenup vs Postnup in Australia
Both are Binding Financial Agreements under Australian law. The difference is timing — and that matters more than you might think.
Same legal framework, different timing
In Australia, both prenups and postnups are created under the Family Law Act 1975 as Binding Financial Agreements. The legal requirements — independent legal advice, written form, signed certificates, voluntary execution — are the same for both.
The difference is simply when the agreement is made:
• A prenup is created before marriage or before a de facto relationship begins • A postnup is created during a marriage or established de facto relationship
Both can be legally binding. Both involve the same core process.
Why timing affects the conversation
While the legal requirements are the same, the emotional and practical context is quite different.
A prenup is created before the couple's finances are intertwined. There is typically more clarity about what each person is bringing to the relationship. It is easier to document separate property when the relationship is new.
A postnup is created after financial lives have merged to some degree. Property may have been purchased together. Income may have combined. Teasing apart what is separate and what is joint requires more care — and often more detailed legal work.
This does not mean postnups are harder to execute legally. But the financial picture tends to be more complex.
Why couples consider a postnup
Couples create postnups for a range of reasons:
• They did not get around to a prenup before the wedding and want to formalise arrangements now • One partner starts or acquires a business during the relationship • A significant inheritance is received and the couple wants to confirm its treatment • Financial circumstances change substantially — one partner's income grows significantly, or debts arise • The couple wants to update an older agreement that no longer reflects their situation • One partner wants to return to work after caring for children, and both want clarity about how finances will be treated going forward
Creating a postnup is a reasonable and practical decision. It is not a sign that a relationship is in trouble.
Can a prenup be replaced?
Yes. A BFA can be replaced or varied by a subsequent BFA. If circumstances change significantly after a prenup is signed — for example, the couple has children, starts a business together, or acquires substantial new property — they may want to update their agreement.
A new agreement can replace the old one entirely, or it can deal with specific matters while the original remains in force for others. Your lawyer can advise on the best approach.
Which is right for you?
If you are planning to marry or enter a de facto relationship, a prenup prepared before the relationship begins gives you the cleanest starting point. Financial disclosure is simpler and the emotional stakes of the conversation tend to be lower.
If you are already married or in a de facto relationship and did not prepare an agreement earlier, a postnup is entirely appropriate. The process is the same — structured financial disclosure, independent legal advice, proper execution.
Premuply is designed primarily for couples at the prenup stage, though the platform's financial disclosure process is equally useful for couples preparing a postnup.