Some pregnancy tests detect a smaller amount of hCG, such as First Response. Others require a higher level of hCG to get a positive result. So, they do differ. The dollar tree brand is just as sensitive, and just as accurate as pricier brands like 1st Response. Some women can take up to 2 weeks or a month after missing their period to test positive. hCG levels vary greatly. If you are really late, I would recommend going to the Dr for a blood test. Also, there’s a possibility that you may have ovulated late, which in turn would make your period late. Ovulation determines the length of your cycle and determines the day your period is going to come. If you ovulate late, your period will be late. A blood test is the tell all, and if not pregnancy, the Dr will try to get to the bottom of what’s going on. In rare cases, some women never test positive on an hpt. Good luck to you and lots of baby dust!!