I usually try to make myself wait until after a missed period, however I can get a bit crazy from the wait and that sometimes doesn't work out that well haha. It's hard for me to figure out when to test sometimes because my periods can be sort of wacky and don't seem to follow a set number of days from month to month, one cycle will be 30, the next will be 40. It's a headache that's for sure. If you are regular though I'd recommend waiting until after a missed period or just before you expect one at the very least. With my daughter I tested positive a couple days before my period was due so it can happen, that was with a first response test. If testing early get a sensitive one like gardenofedens said.