What happens if a Prenuptial Agreement is not signed before marriage in California?

If a Prenuptial Agreement is not signed before marriage, in California, it is not valid. It may still be possible to enter into a Postnuptial Agreement after marriage based on the same or similar terms in the Prenuptial Agreement. However, it is advisable to consult with an attorney to understand the legal implications involved in such a process because once married, each has fiduciary duties to the other spouse, which impact the requirements for a Postnuptial Agreement.