A period is considered late when it arrives five or more days after you expected it based on your usual cycle. If you go more than six weeks without a period, it’s classified as missed rather than simply late. Most people experience a late period at some point, and the causes range from something as straightforward as stress to underlying hormonal conditions that benefit from medical attention.
Pregnancy Is the First Thing to Rule Out
If you’re sexually active, pregnancy is the most common reason for a suddenly late or missed period. Home pregnancy tests are about 99% accurate when used correctly on or after the day your period was expected. Testing before that point can produce a false negative because hormone levels may not be high enough to detect yet. If you get a negative result but your period still hasn’t arrived a few days later, test again.
How Stress Delays Your Cycle
Stress is one of the most common non-pregnancy reasons for a late period, and the biology behind it is well understood. When you’re under physical or emotional stress, your body produces more cortisol. That cortisol doesn’t act on your reproductive hormones directly. Instead, it targets a group of specialized nerve cells in the brain that normally stimulate the release of reproductive hormones. Cortisol dials down the signals these cells send, which reduces the hormonal pulses your ovaries need to prepare and release an egg.
Without that signal, ovulation can be delayed or skipped entirely, pushing your period back by days or even weeks. This can happen during periods of intense work pressure, grief, sleep deprivation, illness, or major life changes like moving or starting a new job. Once the stressor resolves and cortisol levels normalize, cycles typically return to their usual pattern within one to three months.
Undereating and Overexercising
Your body needs a minimum amount of energy to sustain a menstrual cycle. When you’re burning significantly more calories than you’re consuming, whether through restrictive eating, intense training, or both, your brain interprets that energy deficit as a threat and suppresses reproductive function. This is part of what’s known as the Female Athlete Triad: low energy availability, menstrual disruption, and weakened bones.
There’s no single calorie threshold that triggers this for everyone. Research has found significant individual variability in how much of an energy deficit it takes to disrupt someone’s cycle. What matters is the overall pattern: the greater the gap between what your body needs and what it’s getting, the more likely your period is to become irregular or disappear. Rapid weight loss, even without exercise, can produce the same effect. Restoring adequate nutrition is typically enough to bring cycles back, though it can take several months.
Polycystic Ovary Syndrome (PCOS)
PCOS is one of the most common hormonal conditions in people of reproductive age and a frequent cause of chronically irregular periods. The 2023 international guidelines define irregular cycles as those shorter than 21 days or longer than 35 days, or fewer than eight cycles per year (for anyone more than three years past their first period). If your cycles consistently fall outside those ranges, PCOS is one of the first things worth investigating.
PCOS involves an imbalance in reproductive hormones that can prevent eggs from maturing or being released on schedule. Other signs include acne, excess hair growth on the face or body, thinning hair on the scalp, and difficulty losing weight. Not everyone with PCOS has all of these symptoms. A healthcare provider can evaluate you with blood work and, in some cases, an ultrasound. Treatment focuses on managing symptoms and can include hormonal contraceptives, lifestyle changes, or medications that help regulate ovulation.
Thyroid Problems
Your thyroid gland controls your metabolic rate, and when it produces too much or too little hormone, your menstrual cycle is often one of the first things affected. An underactive thyroid tends to cause heavier, more frequent, or prolonged periods, while an overactive thyroid more often leads to lighter, less frequent, or skipped periods. Both can make your cycle unpredictable. Thyroid issues are diagnosed with a simple blood test, and treatment with medication typically restores regular cycles.
Coming Off Hormonal Birth Control
If you’ve recently stopped using hormonal contraception, a delayed period is normal and expected. How long it takes depends on the method you were using. After stopping the pill, hormone levels drop within about 36 hours, and most people get a period within a few weeks, though it may take up to three months for cycles to fully regulate. Hormonal IUD removal produces a similarly quick hormonal reset.
The exception is the injectable shot, which is designed to suppress ovulation for three months at a time. After your last injection, it can take seven to nine months for the medication to fully clear your system and for ovulation to resume. If your period hasn’t returned within three months of stopping the pill or having a device removed, it’s worth checking in with your provider to make sure nothing else is going on.
Perimenopause
If you’re in your mid-to-late 40s and your periods have become unpredictable, perimenopause is a likely explanation. This transition to menopause typically starts in a person’s mid-40s and lasts about four years on average, though the range is two to eight years. During this time, you may not ovulate every month, which means periods can arrive early, late, or not at all for stretches. Flow can be heavier or lighter than you’re used to, and cycle length can swing from unusually short to unusually long.
The average age of menopause in the United States is 52, with most people reaching it between 45 and 58. Once you’ve gone 12 consecutive months without a period, you’ve reached menopause. Until then, the irregularity is a normal part of the transition, though very heavy bleeding or cycles that become suddenly much shorter deserve medical attention.
Other Medical Causes
Several other conditions can delay or stop your period. Elevated levels of prolactin, a hormone normally associated with breastfeeding, can suppress ovulation even when you’re not pregnant or nursing. Premature ovarian insufficiency, where the ovaries stop functioning normally before age 40, is less common but causes missed periods along with symptoms similar to menopause. Uncontrolled diabetes and celiac disease can also interfere with cycle regularity, as can certain medications including some antidepressants and antipsychotics.
When a Late Period Needs Attention
A period that’s a few days late once or twice a year is rarely a sign of anything concerning. But certain patterns call for evaluation. If you’ve had regular cycles and your period is missing for more than three months, that meets the clinical definition of secondary amenorrhea and warrants investigation. If your cycles have always been irregular and you go six months without a period, that also crosses the threshold for follow-up. For adolescents, not getting a first period by age 15 (or within five years of the start of breast development) is a reason to see a provider.
Tracking your cycle for a few months, even with a simple calendar, gives you and your provider useful data. Knowing your typical cycle length makes it much easier to distinguish a one-off late period from a pattern that points to something worth treating.