A period is considered late when it arrives five or more days after you expected it, and officially “missed” once six weeks have passed with no bleeding. Pregnancy is the most common reason, but dozens of other factors can throw off your cycle. Most fall into a few major categories: hormonal conditions, body weight and energy balance, stress, medications, and age-related changes.
Stress and Your Cycle
Stress is one of the most common and most overlooked reasons for a late period. When your brain perceives sustained physical or emotional stress, it can suppress the hormonal signal that triggers ovulation. No ovulation means no progesterone surge, which means your uterine lining doesn’t get the cue to shed on schedule. The delay can range from a few days to a fully skipped cycle.
This isn’t limited to major life crises. A rough month at work, poor sleep, jet lag, or even an illness like the flu can be enough. The period typically returns to normal once the stressor resolves, though it can take a cycle or two to recalibrate.
Polycystic Ovary Syndrome (PCOS)
PCOS is one of the most common hormonal disorders in women of reproductive age, and irregular periods are its hallmark feature. The condition involves higher-than-normal levels of androgens (often called “male hormones,” though all women produce them). These elevated androgens can prevent your ovaries from releasing an egg each month, which delays or skips your period entirely.
Clinically, cycles longer than 35 days or fewer than eight cycles per year are considered irregular in the context of PCOS. Some people go 90 days or more between periods. Other signs include acne along the jawline, thinning hair on the scalp, and excess hair growth on the face, chest, or back. Not everyone with PCOS has all of these symptoms, and the condition looks different across ethnicities. A diagnosis requires at least two of three features: signs of excess androgens, irregular ovulation, and a specific ovarian appearance on ultrasound.
PCOS is manageable. Hormonal birth control can regulate cycles, and lifestyle changes like maintaining a stable weight often improve ovulation on their own. If you’ve had persistently irregular cycles along with any of the symptoms above, it’s worth bringing up with your doctor.
Thyroid Problems
Your thyroid gland, the small butterfly-shaped gland at the front of your neck, has a surprisingly direct influence on your menstrual cycle. It interacts with your ovaries and affects a protein called sex hormone-binding globulin (SHBG) that carries reproductive hormones through your bloodstream.
When your thyroid is underactive (hypothyroidism), your body produces excess amounts of a hormone called prolactin. Too much prolactin interferes with your ovaries’ ability to produce estrogen, which can cause infrequent or completely absent periods. Some people also notice unexpected milky breast discharge, hot flashes, or vaginal dryness. When the thyroid is overactive (hyperthyroidism), elevated SHBG levels can prevent ovulation, leading to similar cycle disruptions.
Thyroid disorders are diagnosed with a simple blood test, and treatment typically brings periods back to a regular pattern within a few months.
Low Body Weight and Excessive Exercise
Your body needs a certain amount of energy and body fat to sustain a menstrual cycle. When the balance tips too far, whether from calorie restriction, an eating disorder, intense athletic training, or some combination, your brain essentially shuts down the reproductive system to conserve resources. This is called hypothalamic amenorrhea.
It works like this: the hypothalamus, a region in your brain that acts as a hormonal control center, stops sending the signals your ovaries need to develop and release eggs. Without ovulation, your period stops. It’s not usually a single factor but a combination: exercising heavily while not eating enough, chronic dieting, or rapid weight loss. Athletes in sports that emphasize leanness (distance running, gymnastics, ballet) are particularly susceptible.
Recovery involves eating enough to meet your body’s energy demands and, in some cases, reducing exercise intensity. Periods often return once your body reaches a healthy, stable weight, though the timeline varies from person to person.
Sudden Weight Gain
Weight gain can disrupt your cycle too, though through a different mechanism. Fat tissue produces estrogen. When body fat increases significantly, the extra estrogen can interfere with the normal hormonal fluctuations that drive ovulation. This sometimes results in longer cycles, heavier bleeding when your period does arrive, or skipped periods altogether. The effect is particularly pronounced when weight gain happens quickly.
Medications That Delay Periods
Several categories of medication are known to disrupt menstrual timing. Hormonal contraceptives are the most obvious: some birth control pills, hormonal IUDs, implants, and injections are specifically designed to lighten or eliminate periods. But non-hormonal medications can do it too.
- Antipsychotics and some antidepressants can raise prolactin levels, which suppresses the hormonal chain reaction needed for ovulation.
- Chemotherapy and radiation therapy can damage ovarian tissue directly, sometimes temporarily and sometimes permanently.
- Blood pressure medications and certain allergy medications can also disrupt hormone balance enough to delay or stop periods.
If your period became irregular after starting a new medication, that’s a connection worth discussing with your prescriber. In many cases, adjusting the dose or switching to an alternative resolves the problem.
High Prolactin Levels
Prolactin is the hormone responsible for breast milk production, but it plays a role in non-pregnant people too. When prolactin stays elevated (a condition called hyperprolactinemia), it suppresses the brain’s release of the hormones that trigger ovulation. Specifically, high prolactin dampens the pulses of luteinizing hormone and follicle-stimulating hormone your ovaries rely on to develop and release eggs. The result ranges from irregular cycles to periods disappearing entirely.
The most common cause is a small, benign growth on the pituitary gland called a prolactinoma. Medications (especially antipsychotics) are another frequent trigger. Hypothyroidism can raise prolactin too, which is one reason thyroid screening is standard when someone reports missed periods. Prolactin levels are checked with a blood test, and the condition is usually very treatable.
Perimenopause
If you’re in your 40s and your previously reliable cycle has started behaving unpredictably, perimenopause is a likely explanation. This transitional phase before menopause typically begins in the mid-40s, though some women notice changes as early as their mid-30s or as late as their 50s.
During perimenopause, estrogen and progesterone levels fluctuate erratically rather than following their usual monthly pattern. You may skip ovulation in some months, which means no period or a very late one. Cycles might be shorter for a while, then longer, then skip entirely for a month or two before returning. This phase lasts an average of four to eight years before periods stop permanently (menopause). Other common signs include hot flashes, sleep disruption, and mood changes.
Chronic Illness
Certain chronic conditions can quietly affect menstrual regularity. Poorly controlled diabetes alters insulin and hormone levels in ways that disrupt ovulation. Celiac disease, an autoimmune reaction to gluten, is associated with absent or rare menstruation at more than twice the rate seen in the general population (roughly 4.6% compared to 2%). Inflammatory bowel disease, kidney disease, and other conditions that cause systemic inflammation or nutritional deficiencies can have similar effects.
In many of these cases, getting the underlying condition under better control brings cycles back to a more predictable rhythm. If your periods became irregular around the same time you developed other new symptoms, like digestive issues, unexplained fatigue, or significant changes in weight, the two may be connected.
Coming Off Hormonal Birth Control
After stopping hormonal contraception, especially long-acting methods like injections, it can take several months for your natural cycle to resume. Your body needs time to restart its own hormonal signaling after relying on synthetic hormones. Most people see their period return within one to three months after stopping the pill. Injectable contraceptives can delay the return of fertility and regular periods for six months or longer.
This is normal and doesn’t indicate a problem on its own. However, if your period hasn’t returned within three months of stopping oral contraception (or within a reasonable window for your method), it’s worth getting evaluated to rule out an underlying condition that the birth control may have been masking, like PCOS.
How Many Missed Periods Warrant a Checkup
A single late or skipped period after a negative pregnancy test is rarely cause for concern, especially if you can point to an obvious trigger like a stressful month, a new medication, or a recent illness. Two or more missed periods in a row is the threshold where medical guidelines recommend getting evaluated. A basic workup typically includes blood tests to check thyroid function, prolactin, and androgen levels, along with a review of your medical history and any medications you’re taking. Most causes of late periods are highly treatable once identified.