Late!

Ok, I'm trying not to get too excited but my period is four days late! Me and my fiancé have been ttc since February and this is the first time I've been late. When should I take a test? I've been told different things, ie it's too early, yet I saw a post on here of a woman who was three days late and she had a positive test. I'm so nervous but excited and feeling a little impatient waiting lol