How do you know when you're not contagious (from a cold, in my case) anymore? I've got dance class tonight, and i desperately want to go. But I'm not going if I could give this cold to other people. But how do you know when you're not contagious anymore? From friends who have gotten this before me, I know this cold has long-lasting symptoms (fatigue, head congestion) even when it seems as if the illness itself has passed.