Unless you are extremely regular with your cycle it's probably not late, you may have just ovulated later than you thought but it wouldn't hurt to take a test just to be sure.
There's a few of things to consider as to why your period is late. One, you may have ovulated later than normal due to an illness, new exercise regimen, stress, etc., thus your period is late. Second, if you in fact ovulated as usual, you may be experiencing a chemical pregnancy (early term miscarriage). Third, you may have an off cycle due to increased levels of progesterone leading to a longer luteal phase. Or fourth, this may be whats called an "anovulatory cycle" when there's no ovulation, but the lining still builds up and sheds itself. Anovulatory cycles tend to be longer.
If your period is at its normal flow, an HPT probably would have a BFN response. Even if you experience a chemical pregnancy, the hCG hormone is probably too low to detect on the HPT. I hope your next cycle is back on track!