7 Logical Reasons Your Period Might Be Late

Why Is My Period Late?

Having a late period is never a relaxing experience, even if you've taken 10 pregnancy tests or are otherwise a 1,000,000% sure you're not eating for two. The uncertainty of what the heck is going on with your body is the unsettling part. "Why is my period late?!?" you want to scream into the sky.

Of course, when something's off with your cycle, making an appointment with a gynecologist or reproductive health specialist you trust is a necessary and responsible move. But if your appointment is still an agonizing week away and you're stressing about it, we've got you. We spoke to the lovely and reliable Leah Millheiser, an ob-gyn at Stanford University, to get her opinion on the seven most common reasons for a late period other than pregnancy. Again, definitely go to the gyno if you have a mysteriously late period, but in the meantime, here are some ideas for what might be causing it.

Polycystic Ovary Syndrome

PCOS is a condition that affects a woman or ovary-owning person's hormonal system, usually causing them not to ovulate every month. Because one has to ovulate to get a period, someone with PCOS might not get a period at all or might have irregular periods where they only get one every few months (again depending on how often they ovulate). PCOS is a common condition, affecting 10% to 15% of people with ovaries. (You can read way more details about it here!)


If you're missing periods and have been pushing your body to a fitness extreme lately, there could be a connection there. Excessive exercising can cause one to develop something called hypothalamic amenorrhea, Millheiser explains. This is a condition that affects the hypothalamus in such a way that you don't produce the hormones necessary for ovulation and, thus, a period.

Calorie Restriction

Under-eating or anorexia can also cause hypothalamic amenorrhea and a loss of menstruation, says Millheiser. In fact, missing periods for at least three months is one of the first diagnostic criteria for anorexia. When one loses at least 15% of their normal body weight, fat stores reduce, throwing reproductive hormones all out of whack and causing one's period to become much lighter or stop altogether.

Emotional Stress

Physical stress like over-exercising and under-eating aren't the only causes of hormonal hijinx. "If somebody is under a great deal of emotional stress, it can affect the brain function responsible for hormonal regulation," Millheiser comments. That can include anxiety, work pressures, or even an intense life event like a move or breakup. Hormones can be sensitive to all those factors.

Birth Control

Millheiser encourages us to consider medication as a cause of hormonal changes and missed periods—and birth control definitely counts as medication. Some folks who take birth control pills regularly might get a really light period or no period at all during their placebo week. (Or, obviously, you could be skipping your sugar pills so you don't get a period on purpose.) Missed periods also commonly happen with hormonal IUDs and, as long as you're sure you're not pregnant, should be no cause for concern.


A microadenoma is a benign (read: noncancerous) tumor in the pituitary gland of the brain that causes an overproduction of the hormone prolactin, which causes a suppression of regular hormonal function, and sometimes people who have these benign tumors lose their periods, Millheiser explains. Microadenomas are actually surprisingly common (they affect about one in six of the general population), but the ones that require surgery to fix are rarer, affecting more like one in 1000. Though these slightly more serious tumors don't happen as often, Millheiser says they're definitely still one of the first things screened for when someone comes in with a missed period (caused by something other than pregnancy).

Early Menopause

Premature menopause, also known as primary ovarian insufficiency, only happens about 1% of the time, but it's still a cause worth considering. This is where a woman goes through menopause before the age of 40 (the average age is 51). It can happen as young as your teens (though that's rare) or in your 20s and 30s. "It's essentially when your ovaries stop working, and it can be caused by genetics, autoimmune disorders, or a certain karyotype [or chromosomal] issue like Turner Syndrome," says Millheiser.

Whether you think your missed period is caused by something on this list (or something rarer), definitely go hang out with your gyno and get their professional opinion. Best of luck figuring out why Aunt Flo isn't coming around much these days!

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