A period is considered late when it arrives five or more days after your expected start date. If you’ve gone six weeks or longer without bleeding, it’s classified as a missed period. Pregnancy is the most common reason, but it’s far from the only one. Stress, weight changes, hormonal conditions, medications, and even jet lag can all push your cycle off schedule.
Pregnancy
If you’re sexually active, pregnancy is the first thing to rule out. Home pregnancy tests claim more than 99% accuracy when used from the day of your expected period, but that accuracy depends on the test being sensitive enough to pick up very low levels of the pregnancy hormone in your urine. Some tests need a higher concentration than others, so if you get a negative result but your period still hasn’t arrived a few days later, testing again gives you a more reliable answer.
Stress
Your brain controls when you ovulate, and stress can directly interfere with that signal. When you’re under sustained pressure, your body produces more cortisol, the primary stress hormone. Elevated cortisol suppresses the hormonal pulse that triggers ovulation, and it does so at the level of the brain itself rather than the ovaries. Without ovulation happening on time, your entire cycle shifts later.
This doesn’t require a major life crisis. A demanding stretch at work, poor sleep for a couple of weeks, or an illness can produce enough cortisol to delay things. The period typically returns to normal once the stressor passes, though it can take a cycle or two to fully reset.
Undereating or Rapid Weight Loss
Your body tracks whether you have enough energy to support a pregnancy, and it uses a hormone called leptin as the gauge. Leptin levels are directly proportional to your fat mass. When those levels drop too low, your brain dials down the same ovulation signal that stress disrupts. This is why crash diets, intense exercise programs without adequate fueling, and eating disorders are strongly linked to late or absent periods.
Leptin operates in a surprisingly narrow range. Too little shuts down your cycle, but too much (as often happens with obesity) can cause resistance to the hormone’s signal, which also compromises fertility and cycle regularity. The sweet spot for normal ovarian function falls within a relatively tight window, which helps explain why significant weight gain can delay periods just as weight loss can.
Polycystic Ovary Syndrome (PCOS)
PCOS is one of the most common hormonal conditions in women of reproductive age, and irregular or late periods are a hallmark. It’s diagnosed when at least two of the following three features are present: elevated androgen levels (sometimes visible as excess facial hair or acne), irregular ovulation, and a characteristic appearance of the ovaries on ultrasound. If you have both irregular cycles and signs of high androgens, that alone is enough for a diagnosis without any imaging.
PCOS doesn’t mean your ovaries have cysts in the traditional sense. The “cysts” are actually small, immature follicles that haven’t released an egg. Because ovulation is inconsistent, periods can arrive weeks late or skip entirely. If your periods have been unpredictable for a long time rather than just this one cycle, PCOS is worth investigating with a healthcare provider.
Thyroid Problems
An underactive thyroid can delay your period through a chain reaction of hormonal changes. When thyroid hormone levels are low, your brain ramps up production of a hormone meant to stimulate the thyroid. That same hormone also triggers a rise in prolactin, which is normally elevated during breastfeeding and is designed to suppress ovulation. So hypothyroidism essentially mimics a low-grade version of the hormonal state that keeps breastfeeding women from getting pregnant. An overactive thyroid can also throw off your cycle, though the mechanism is different. Either way, a simple blood test can identify the problem.
Medications
Several types of medication can delay or stop periods as a side effect. Hormonal birth control is the most obvious, especially after stopping it, when it can take a few cycles for your body to resume its natural rhythm. But non-contraceptive drugs can do it too. Antipsychotic medications are particularly notable: studies have found that 11 to 35% of women taking them experience missed periods, with some drugs carrying a higher risk than others. The mechanism usually involves raising prolactin levels, the same hormone that links thyroid problems to late periods.
Circadian Rhythm Disruption
The hormonal surge that triggers ovulation follows a circadian pattern. In most women, the surge peaks between midnight and 8 a.m. When your internal clock gets scrambled by jet lag, shift work, or irregular sleep schedules, that surge can be delayed or blunted.
Research on shift workers shows that women working night or rotating shifts report changes in cycle length, heavier or lighter bleeding, and more menstrual pain. These symptoms come with measurable changes in hormone secretion, including a longer follicular phase (the first half of the cycle before ovulation). Frequent travelers crossing time zones may be even more affected than shift workers, because their light exposure is constantly changing and their bodies never fully adjust.
Perimenopause
If you’re in your 40s and your periods are becoming less predictable, perimenopause is a likely explanation. Some women notice changes as early as their mid-30s. In early perimenopause, cycle length starts varying by seven days or more from month to month. In late perimenopause, gaps of 60 days or longer between periods become common. This transition typically lasts several years before periods stop entirely.
When Late Becomes a Medical Concern
A single late period is rarely a sign of something serious. But if you’ve missed three consecutive cycles and you previously had regular periods, or you’ve gone six months without a period and your cycles were already irregular, that crosses the clinical threshold for secondary amenorrhea, a condition that warrants evaluation. Blood work can check for pregnancy, thyroid dysfunction, elevated prolactin, and androgen levels, which together cover the most common causes. Knowing why your cycle has stopped matters, because some causes, like low estrogen from undereating, can affect bone density and long-term health even if the absence of periods feels like a minor inconvenience.