For me, 10 dpo, but I've never tested before then. In both of my pregnancies, I got a first positive at 10dpo and then 12dpo, but the lines were strong enough that I probably would have seen something at least a day or maybe two before. But I don't test before I feel pregnant, so I've never been an early tester. Personally, I would avoid testing before 9dpo. Implantation occurs roughly 6-12dpo with 9dpo being the average. If you're testing at 6 or 7dpo, in the absence of obvious pregnancy symptoms, it's very likely implantation hasn't even happened and you're just setting yourself up for stress and disappointment as you won't really get an answer you can feel confident about for a few more days, even if you think you might see something faint. I know it's hard to wait, but it probably saves you stressing yourself out about what you think you may or may not see.