A postnuptial agreement is a marriage contract entered into between married spouses after the actual marriage. According to Legal Nature, the law permits parties contemplating marriage or who are already married to enter into a domestic contract governing certain aspects of their relationship. It is generally less common for married couples to enter into an agreement after marriage.

Typically, these contracts are presented prior to marriage. But there are circumstances where a contract during a marriage can be advisable or there are quite reasonable circumstances. For example, this may be ideal if one of the spouses is about to inherit some money and they might be intending to put some of those funds into the matrimonial home. Normally, if you receive an inheritance during the marriage and you use those funds to pay down your mortgage or improve your home, you will not be able to claim those funds as excluded property if you separate from your spouse. According to FindLaw, to prevent that potentially unfortunate outcome, you would be well advised to ask your spouse to enter into a marriage contract at the time that you receive these funds.

Another circumstance is that of the family cottage. These are often passed on from generation to the next, and if they are received during the marriage and commonly used by the family, it can qualify as a matrimonial home and the exclusion of the gift of the property would not be allowed under the family line. That would be another case where the marriage contract would be advisable. Other reasons for marriage contracts include if one of the parties has a business and perhaps there are other owners in the business, and they wish to exclude that asset from a potential equalization claim.