“Missing period” is such a goofy phrase—as if you could go looking for it! I have a friend who is very upfront about these things. When she was worried that something was up, she went to the drugstore, bought the pregnancy test and then asked to use their bathroom. Her comment to the clerk was “when you gotta know, you gotta know!” Her test was negative, which was a relief to her.

Then she called me to ask if she had tested too soon. Since she had a good grip on her menstrual cycle, and she was testing about week late, it was most likely a reliable result. Sure enough, her period arrived in two days.

Periods can be late for so many reasons. Stress is the biggest one as it can cause delayed ovulation, leading to a longer cycle. It really depends on the woman as to how sensitive her cycle is. Some women are like clockwork no matter what, and others are thrown off easily. If you’re taking birth control pills, and your period does not come at the end of the active pills, that’s a very strong sign that you might be pregnant since the whole idea of oral contraceptives is to prevent ovulation and force a set cycle. Even stress usually does not interfere with the cycle imposed by oral contraceptives.

Top athletes often stop menstruating because their body fat falls too low, usually less than 13% body fat. That is an example of extreme physical stress. College students may find their periods delayed during finals, due to mental stress. And women who are breast-feeding typically ovulate irregularly, resulting in shorter or longer cycles.

Testing on the day you expect your period may lead to a false negative. As hard as it is, you will get a better result by waiting a few more days to test. Even then, if conception occurred, but implantation was not successful, you’ll experience a late period with a negative pregnancy test.

HCG, Human chorionic gonadotropin, is what pregnancy tests are testing for, and some of them are more sensitive than others. It takes a while for HCG to build up, and it doesn’t even start building up until implantation. There is no test that can tell you conception occurred because there is nothing that we can measure for that event. Even a blood test for pregnancy is measuring a certain amount of HCG in you, and while that will be detectable before it is detectable in urine, it’s still not instantaneous.

That’s why most doctors are not interested in seeing you for a urine pregnancy test until you are late by at least a week. If you insist on a blood test, they will see you on the day your period is expected. If at any time, however, you experience pain in your abdomen, call your doctor because that can be a sign of an ectopic pregnancy, which is life-threatening. Even if your home pregnancy test is negative, pain means something is wrong, and ectopic pregnancies may register lower than normal levels of HCG.

Since pregnancy tests are not cheap, waiting a few more days to test will save you money and, frankly, anxiety, because would you really believe it if you tested positive (or negative) a few days before your period? Probably not—-you would test again and again and again. That’s why test boxes come with at least two tests, and even that isn’t enough for women who really want to know! Just realize that if you test a week late, your result will be quite reliable.