Parents are super religious and are against premarital sex...

My parents still think I'm religious and have the same world views as them-- I don't. I have a boyfriend of 6 months who they know about, but they don't know we're having sex. I want to eventually move in with him someday, maybe between a year or two, to try it out. But then my parents will find out we're sexually active. How should I go about telling them? Should I tell them now? Wait to tell them later? Have them find out through the grapevine/get the hint through my actions I'm sexually active? Wait till my SO and I are about to move in?