Your best accuracy to get reliable results from a pregnancy test is doing the pregnancy test after you miss your period.
First Response (the test that advertises "99% accurate. Our most accurate results 5 days sooner"), says the following regarding it's accuracy: "4 days before your period, the test is 63% accurate; 3 days before your period 83% accurate; one and two days before 93% accurate." So it's most accurate around the time you miss your period.
When you do a pregnancy test too early, you may get a false negative pregnancy test and be disappointed. Waiting until you miss your menstrual period and until your menstrual period is late, maybe 1-2 days late, will save you money and will give you a better chance to prevent a false negative pregnancy test. A healthy mid twenties couple without known fertility problems has a 20% chance each month of getting pregnant. 80% will get pregnant within the first year of trying.