Pretty common, it all just depends on how early in pregnancy the woman begins testing. It also depends on the type of tests she uses. Tests that detect hcg levels at 100 or over typically won't detect pregnancy until a week or more after a missed period in a pregnant woman with hcg levels that double normally. It really just all depends.
If you are a week late for your period and have accurate determined your cycle length, take a first response early result pregnancy test (I'd suggest buying a pack of two). If you get a negative, you have a high chance of not being pregnant, although some women's hcg level isn't high enough yet, but that is uncommon. If you still haven't gotten your period within a week, take the other FRER home pregnancy test. If you get a negative on that, then you can pretty much bet that you are not pregnant.