How should I tell my husband?

I just got my BFP!!!!!! I can't believe I'm finally saying that!!! We've been trying for about a year for our second. I haven't told my husband yet because he's at work. And, tomorrow he leaves early for a business trip for a couple of days. I'm trying to decide if I should tell him tonight before he leaves, or when he gets home Friday afternoon... I just don't know if I can wait that long!! I wanted to surprise him by getting a "Big Brother" shirt for my 2 year old son to wear when he gets home from work. Anyone have any ideas??