I had a 'feeling' I was pregnant 6 days before AF was due, the feeling was so strong that I told my husband I'm sure I am pregnant, I bought HPT and tested 5 and 3 days before AF was due but both came back negative so I was patient and waited until the day I was due and tested again that morning. I was delighted when that second line appeared, I burst into tears and couldn't wait to share the news with my family (it was extra special to find out when we did because we were in Oz visiting my Dad, Bro and Grandparents so it was lovely being able to tell them our exciting news in person instead of over the phone).
When I was pregnant with my daughter though (2 years ago) I didn't have a clue and I didn't test until a week after my period was late.