I just got my BFP, can someone help me figure my due date?

So I am 13 DPO today so does that make me 2weeks preg or do you take it back to start of cycle? if so that was over 42 days ago!! My cycles are really long. So if I take it back to first day of AF I am 6weeks pregnant even though I only concieved 14 days ago??!! Confused......confused but Super happy :)