I didn't get my bfp until 17 DPO. My period was due September 16th (last year). Tested three days before, negative. Tested day after period was due, negative. Eventually I figured I was just skipping my period and stopped testing for a few days until I had a feeling I should test one more time and there it was! I was 8 days late. I will add, however, that I have abnormally long cycles and this doesn't happen all the time. But if you have long cycles like me, you can implant later than average. (For example, my doctor told me I didn't even implant until day 13/14)... that being said--- I always recommend waiting as long as you can! But to also be knowledgeable about your self and your cycles. Good luck!