“Take the test at least one day after a missed period,” says ob-gyn Lauren Streicher, MD. Any sooner and you might get wishy-washy results, especially if you conceived late in your cycle and the egg is still traveling down the fallopian tube. If the test is negative and you still don’t get your period within a week, take another one to be sure, says Dr. Streicher. Keep in mind that with drugstore pee sticks, the time of day that you use them matters. Do it the first time you pee in the morning, when your urine is concentrated and you can be positive it’s a solid read.