You can take it the day of your missed period. So if you dont start your period the day you are supposed to, take it that day. The results may be negative, but try again in another week. Some tests are pretty expensive, so I would shop around. I know that First Response Pregnancy Tests, have a product that has 3 tests in it. Thats the best choice to make I think. So you can take 2 more tests to make sure you didnt get a false possitive. I took 5 tests, 2 were negative, the other 3 were just because I was excited and wanted to see the positive again!