have you been stressed lately? that can attribute to a late period. Or medications may affect your cycle. or, perhaps you have a close friend and your cycles are syncing up? there are a lot of factors that can affect your period.
I would say if you don't see it in 3-4 days to retest. Sometimes your hcg levels aren't high enough for the home pregnancy tests.
if you don't get it and its still negative perhaps consider going to see your doctor.