5 months. Easiest way for me to keep track is to go up a month every month on the day I'm due.
So I see your EDD is May 18th. On the 18th of every month, you're another month pregnant (Feb 18th- 6 months. March 18th- 7 months etc.) It's not as exact as weeks to months conversion, but it works in a pinch when someone asks how many months you are