A post-nuptial agreement (also called a post-nup) is designed to decide what should happen to each spouse’s assets on divorce, just like a pre-nup. However, a post-nup is entered into by you when you are already married, whereas a pre-nup is done before the wedding. A post-nup can be a good thing to consider if you have previously separated but have decided to give the marriage another go and you want to avoid uncertainty if things go wrong again.