A prenuptial agreement is also referred to as a "prenup" or a premarital agreement. It is a contract between two people planning to marry.
The earlier you sign the contract the better. If you sign shortly before the wedding the more possible it may be to argue that the contract was signed under duress or that one of the parties did not have sufficient time to consider the terms. In Illinois, where I practice, the law does not set a specific time limit between signing and the wedding.
In some states you can waive alimony. In Illinois, couples may waive their right to alimony in a premarital agreement. This can be a very valuable term as alimony can amount to hundreds of thousands of dollars. Courts in Illinois can award permanent alimony which means you could be paying your ex for decades.
A premarital contract may not be enforceable unless you and your fiance were represented by separate lawyers. If you use a “do-it-yourself" contract or only one of you had a lawyer, the contract may not be worth the paper on which it was written.
You may specify who gets to keep pets or a visitation arrangement for pets. You may protect yourself from your fiance's debts.
You may agree to compensate a spouse who will not be working during the marriage.
You cannot waive or set child support in a premarital agreement.