Well, you're only breaking even unless you enjoy the biking for its own sake. One hour in the saddle, one hour longer life. Or the other way around: if you hated the cycling but do it for health only, you waste an hour for every hour gained. Fortunately most of us here do enjoy it, and I personally take it in the spirit that every hour riding is an extra hour out of time. Kind of like a two-wheeled Tardis that way.