at least 2 weeks. It takes approx 14 days for the egg to become fertilized, implant into your uterus and send out the hCg hormone (which is what turns a pregnancy test positive). Most like if your period is in less than 2 weeks you aren't pregnant. It's possible not not likely at all. If your period is about 14 days or more away wait until it shows or doesn't show. If it doesn't show then test. If it's negative wait 3 or 4 more days and try again.
Good luck
edit: I forgot to mention: always test with the first urine of the day. It is the most concentrated and will give you the most accurate results. If you test in the afternoon or evening you may get a negative when you are actually pregnant just because of how diluted your urine is.
Also, don't worry about those "early response" tests. They are really just a waste of money since 5 days before your period they are only 65% accurate. They don't reach 99% accuracy until the same time as every other test (the day of your missed period).
