How soon can someone know their pregnant?

Pregnancy: Most women test when they have missed a period but an early pregnancy test can be done a couple days prior to that.

Typically, when you: miss your period, about 14 days after the presumed date of conception. If you were having expensive blood tests (HCG) in a doctor's office, even sooner, but home pregnancy tests are quite accurate 14 days after conception. They may be positive a few days earlier, but if they are negative, you can't be sure they are truly negative. If first test negative and no period, test again in a week.

When you miss a: period do a pregnancy test.