Depends on thte length of your cycle.
According to good ol' babycenter, most home pregnancy tests can pick up sufficient levels of hCG (the hormone that is used to detect pregnancies) about a week after you would normally expect your period.
Here's an excerpt:
Most home pregnancy tests claim to be "greater than 99 percent accurate" and imply that you can use them as early as the day you miss your period, but a study published in 2004 in the American Journal of Obstetrics and Gynecology has shown that this is misleading. The fact is that the amount of hCG in the urine on any given day after implantation can vary a great deal from one woman to another. Laurence Cole and other researchers at the University of New Mexico evaluated 18 currently available tests and found that only one was consistently sensitive enough to detect the levels of hCG that most pregnant women were likely to have on the first day of their missed menstrual period. Most of the other tests were only sensitive enough to pick up about 16 percent of pregnancies at that point,
though many were likely to be accurate a week after an expected period was due. ***
Apparently, the First Response Early Result pregnancy test is the one that can do the earliest detection. On their web site, they boast that their test is sensitive enough to pick up pregnancy levels of hCG as early as 4 days before an expected period. Your doctor would be able to detect with a blood test shortly after that.
Good luck (assuming you are hoping for a pregnancy!) & happy "peeing on a stick!"
