If you regret not having drafted for your marriage a prenuptial agreement about your finances and other assets and custody etc. then it might still not be too late for you to sign on such a legal agreement. A postnuptial agreement which is similar to a prenuptial agreement in every way except that it is signed after a couple marries; is as valid and as legal and as helpful as any prenuptial agreement would be. There are certain circumstances under which a postnuptial agreement would especially come in handy.
The couples who benefit most out of these postnuptial agreements are those who are almost on the verge of a divorce but are willing to work together towards restoring the relationship. Especially if one partner has already filed for a divorce, it would be helpful if the couple could instead sign on a post-nuptial agreement and then decide to work on the relationship instead. This agreement kind of gives the couple a chance to freely try and reconcile as the postnuptial agreement having been signed means that they already know what they are entitled to gain if the reconciliation does not work out.
Another circumstance where a couple must seriously consider a postnuptial agreement would be in case one partner in a marriage starts their own business or if they join some kind of a family business. A properly legal and valid postnuptial agreement would mean that a divorce would not come in between the smooth operations of the business. This becomes especially crucial if there are other family members or even children involved in the business. Also, if a spouse suddenly comes into the property, this is another circumstance where the postnuptial agreement will be very beneficial in protecting the inheritance. This is applicable to those people who would not want their inheritance to become marital property and to remain as separate property so that it is not counted as a joint marital asset at the time of a divorce. So a legal and properly written postnuptial agreement would easily take care of this issue as well.
Another circumstance where the postnuptial agreement is almost like a God-sent is in cases where couples are in Common Law marriage. Because in such marriages there are lots of shades of gray in records this agreement comes in very handy where joint finances and property and separate property is concerned.