The test should be accurate about a week after your first missed period.So if you're trying to get pregnant, and you had intercourse about two weeks before your period was due (when you were ovulating), your test should be accurate about three weeks later. It's always a good idea to repeat the test a few days after the first, just to make sure. The test detects a certain hormone, hCG, in the urine, and the level of this hormone increases over time if you're pregnant. A home pregnancy test might not detect low levels of hCG early on, but should detect it several days later after the level has gone up.There should be information and instructions inside the package with the home pregnancy test, and you can always call your doctor or a reproductive health clinic for more advice and information. Good luck!