I kept mine a secret from everyone except my SO for about three months. At that point I started to think about why I wasn't telling anyone and a friend from AA suggested that maybe I was "leaving the door open" to drinking by not letting people (friends and family) know. I had to think about that for a few days and then decided to just start telling family that I haven't had a drink in xx days.
I wasn't telling anyone because I was scared I couldn't stay stopped. I think it does leave the door open if it is a complete secret for too long.