Missing a period is very common, even if you’re not pregnant. About 3% to 4% of women of reproductive age experience a skipped period at any given time for reasons unrelated to pregnancy, breastfeeding, or menopause. That may sound like a small number, but it means millions of people deal with this regularly, and the occasional missed cycle is even more widespread than that statistic captures. Most of the time, a skipped period resolves on its own within a cycle or two.
The Most Likely Reasons You Missed a Period
Pregnancy is the first thing most people think of, and it’s worth ruling out early. Home pregnancy tests are most accurate after you’ve already missed your period. If you get a negative result and your period still hasn’t arrived after a few more days, testing again gives you the most reliable answer.
Beyond pregnancy, the most common reasons fall into a handful of categories: stress, changes in weight or exercise, hormonal contraception, and normal life stages like puberty or the years leading up to menopause. Less commonly, thyroid problems or a condition called PCOS can cause ongoing irregularity. In most cases, a single missed period doesn’t signal anything serious.
How Stress Disrupts Your Cycle
When you’re under significant stress, your body produces more cortisol, the primary stress hormone. Cortisol interferes with a chain of hormonal signals that normally triggers ovulation each month. Specifically, it suppresses the brain’s release of the hormone that tells your ovaries to prepare and release an egg. If ovulation doesn’t happen, your period either arrives late or doesn’t come at all that cycle.
This isn’t limited to emotional stress. Physical stress counts too: illness, sleep deprivation, travel across time zones, or a major life change like moving or starting a new job. The effect is usually temporary. Once the stressor passes and your body recalibrates, your cycle typically returns to its normal pattern within one to three months.
Exercise, Dieting, and Energy Balance
Your body needs a minimum amount of available energy to maintain a regular cycle. For most active women, that threshold sits around 45 calories per day per kilogram of lean body mass. When energy availability drops below roughly 30 calories per kilogram of lean mass, the body starts shutting down functions it considers non-essential, and reproductive hormones are among the first to be affected.
You don’t have to be a competitive athlete for this to happen. A combination of increased exercise and reduced food intake, even a moderate calorie deficit sustained over weeks, can be enough to delay or skip a period. Rapid weight loss is a particularly common trigger. On the other end of the spectrum, significant weight gain can also disrupt your cycle by altering estrogen levels. The key factor is change: your body responds to shifts in energy balance, not just to being at a particular weight.
Hormonal Contraception Often Causes Missed Periods
If you’re on hormonal birth control, a lighter or absent period may be a side effect of the medication itself rather than a sign of anything wrong. The rates vary dramatically depending on the method. With injectable contraception (the shot given every three months), up to 70% of users stop getting periods after the first year. Hormonal implants cause periods to disappear in about half of users. Progestin-only pills lead to absent periods in roughly 10% to 22% of users.
Combination birth control pills can also cause very light or skipped periods, especially after years of use. This happens because the hormones thin the uterine lining so much that there’s very little to shed. If you’ve recently started, stopped, or switched contraceptive methods, expect some irregularity for the first few months as your body adjusts.
Normal Irregularity at Different Ages
Your age plays a significant role in how regular your cycle is. In the first two to three years after getting a first period, cycles are frequently irregular because the hormonal feedback loop between the brain and ovaries is still maturing. Skipping a month here and there during this time is expected.
On the other end, the transition toward menopause (perimenopause) often begins in the early to mid-40s, though it can start in the late 30s. Early on, cycles may just get slightly shorter or longer. As perimenopause progresses, the gap between periods can stretch by a week or more beyond what’s typical. Eventually, skipping a period altogether becomes routine. In late perimenopause, gaps of 60 days or longer between periods are common. This phase can last anywhere from a few years to a decade before periods stop entirely.
Thyroid Problems and PCOS
An underactive thyroid suppresses the same brain hormone that stress does, reducing the signal that drives ovulation. It also raises levels of prolactin, a hormone that interferes with estrogen production in the ovaries. The result is lighter, less frequent, or absent periods. An overactive thyroid can cause similar disruptions from the opposite direction, often making periods lighter and further apart.
Polycystic ovary syndrome (PCOS) is one of the most common hormonal conditions in women of reproductive age and a frequent cause of chronically irregular periods. PCOS involves a combination of factors: elevated levels of androgens (hormones typically associated with male development), irregular or absent ovulation, and sometimes visible cysts on the ovaries during an ultrasound. If you’re consistently going 35 or more days between periods, or you notice symptoms like excess facial or body hair, persistent acne, or difficulty losing weight, PCOS is worth investigating with a healthcare provider.
When a Missed Period Needs Attention
A single skipped period after a negative pregnancy test rarely requires medical evaluation. Your body is responsive to dozens of variables, and a one-time skip usually corrects itself. The guideline from the American College of Obstetricians and Gynecologists is straightforward: if your period stops for more than three months without a clear explanation, get evaluated. For teenagers, the benchmark is different. A teen should be evaluated if she hasn’t started her period by age 15, or if there are no signs of breast development by age 13.
Three months is the threshold because it gives your body enough time to recover from temporary disruptions like stress, illness, or weight changes. If your cycle hasn’t resumed by then, it suggests something more persistent may be at play, whether that’s a thyroid issue, PCOS, or another hormonal imbalance that benefits from early identification and treatment.
What About Illness and Vaccines
A large study tracking over 5,300 women for 12 months found that neither COVID-19 infection nor vaccination caused meaningful changes in menstrual cycle length. For the small number of participants who did notice a slight shift after infection, the change resolved within one cycle. This is consistent with what’s known about acute illness in general: a fever or viral infection can occasionally delay a period by a few days, but the effect is almost always short-lived.