There is a graph at "countdown to pregnancy" on the Internet that will breakdown what dpo confirmed pregnancies got a positive pregnancy test. The turning point seems to be 10dpo. Earlier than 6dpo is damn near impossible, as the egg takes 5 days to divide/hatch/go through its process, then it has to implant, then your body recognizes it and begins hcg production, which then must double every 24 to 48 hours. So, realistically, I start tentatively testing at 7dpo, and buy super sensitive cheapies, because I'm pyschotic. However, personally, I got a positive at 8dpo, 10dpo, and 11 dpo thus far.