Pregnancy Tests--Late Period
How long is enough time "late" for a period before the pregnancy test is positive?
Q & A: Is being fourteen days late for a period enough time to rely on a pregnancy test?
Generally, yes. In fact, the home pregnancy tests of today are now just about as good* as the urine pregnancy tests done in doctors' offices. Usually, by the time you're even a couple of days late, there is a faint indicator (be it a dot or a line or whatever) that will make the diagnosis of pregnancy likely. A blood test is even more reliable, and earlier, but patience in waiting a few extra days will save you the expense of a doctor's visit and the trouble of a blood test in lieu of the cheaper and private urinary test available over-the-counter.
hCG Pregnancy Hormone
Regarding 14 days, this is more than enough to rely upon in reading a pregnancy test. hCG is the pregnancy hormone read in these tests, specifically, that particular molecule of the hCG called the "Beta-chain." The sensitivity of the test relies on how little beta-hCG can be discerned. I'm sure some brands are better than others, but I don't think by more than a day or two in the earliest "Positive"-reading capability.
I say "about as good," only because the slight increase in inaccuracy in a home pregnancy test takes into account the statistics which include procedural error on the part of the person doing it. In a doctor's office, it'll be done right (we expect) every time.