A late period is one that arrives five or more days after you expected it based on your usual cycle length. If no period comes for six weeks or longer, it’s considered a missed period. While pregnancy is the most common reason, dozens of other factors can push back ovulation and delay bleeding, from everyday stress to underlying health conditions.
Pregnancy
The first thing most people think of is pregnancy, and for good reason. A fertilized egg implanting in the uterine lining stops the normal hormonal cascade that triggers a period. If there’s any chance you could be pregnant, a home test taken after the first day of a missed period gives the most accurate result. Some tests are more sensitive than others, but all of them work by detecting a hormone that only rises after implantation. Testing too early, before your period is actually late, increases the chance of a false negative.
Stress
Your brain is the starting point for your entire menstrual cycle. A region in the brain sends a signal to the pituitary gland, which then tells the ovaries to mature and release an egg. Stress hormones, particularly cortisol, can suppress that initial brain signal at multiple points in the chain. High cortisol levels reduce the hormones that trigger ovulation, and without ovulation, your period gets pushed back.
This isn’t limited to extreme emotional crises. A demanding stretch at work, a move, grief, sleep deprivation, or even excitement about a major life event can be enough. The delay usually resolves once the stressor passes, though it can take a full cycle or two for things to normalize.
Changes in Weight or Exercise
Your body needs a certain amount of available energy to keep the reproductive system running. When you’re burning significantly more calories than you’re taking in, whether through intense exercise, restrictive eating, or rapid weight loss, the brain dials down reproductive hormones to conserve energy. This is especially common in athletes, dancers, and people in physically demanding training programs.
There’s no single calorie threshold that applies to everyone. Research shows that individual susceptibility varies widely: some people lose their period with a moderate calorie deficit, while others tolerate a larger one without disruption. The pattern tends to work on a sliding scale, where the bigger the energy gap, the more likely your cycle will be affected. Significant weight gain can also delay periods by altering hormone balance, particularly by increasing estrogen production from fat tissue.
Polycystic Ovary Syndrome (PCOS)
PCOS is one of the most common hormonal conditions in people of reproductive age, and irregular or late periods are a hallmark symptom. In PCOS, the ovaries may produce higher-than-normal levels of androgens (often called “male hormones,” though everyone has them). This can prevent eggs from maturing and releasing on schedule, which delays or skips periods entirely.
Diagnosis requires two of three features: signs of excess androgens (like acne, thinning hair, or excess body hair), irregular ovulation, and either a characteristic appearance of the ovaries on ultrasound or elevated levels of a specific ovarian hormone. If your periods are consistently unpredictable and you notice any of these other signs, PCOS is worth investigating.
Thyroid Problems
Both an underactive and overactive thyroid can throw off your cycle. The thyroid gland and the reproductive system share overlapping hormonal pathways. When thyroid hormone levels are too low, the brain compensates by releasing more of a stimulating hormone that, as a side effect, can raise prolactin levels. Elevated prolactin interferes with ovulation, which is one reason hypothyroidism often causes late or missing periods. An overactive thyroid can also disrupt the balance of sex hormones and binding proteins that keep cycles regular.
Thyroid issues are straightforward to detect with a blood test and typically respond well to treatment, after which cycles often return to normal.
Stopping Hormonal Birth Control
If you recently stopped the pill, patch, shot, or another hormonal method, your body may need time to resume its own ovulation cycle. In a large study of people coming off oral contraceptives, 89% began menstruating within 60 days. About 7% took 180 days or longer. In rare cases (around 2.2%), the gap stretched much further, though all participants did eventually menstruate on their own.
Hormonal IUDs and the injection can cause especially long delays because they suppress the uterine lining or ovulation more aggressively. A few months of irregularity after stopping any hormonal method is normal, not a sign that something is wrong.
Medications That Affect Your Cycle
Several categories of medication can delay periods as a side effect, usually by raising prolactin levels or changing androgen balance. The most common culprits include:
- Antipsychotics and some antidepressants: These can block dopamine receptors in the pituitary gland, causing prolactin to rise and suppressing ovulation.
- Certain blood pressure medications and anti-nausea drugs: These work through a similar dopamine-blocking mechanism.
- Anti-seizure medications: Some, like valproate, can increase androgen levels and mimic a PCOS-like hormonal pattern.
- Opioids: Both prescription and illicit opioids can elevate prolactin and suppress the hormonal signals needed for a regular cycle.
If you started a new medication and your period became late or disappeared, the medication is a likely contributor. Don’t stop taking it without talking to your prescriber, but it’s worth flagging the change.
Perimenopause
Perimenopause, the transitional phase before menopause, typically begins in the mid-40s but can start as early as the mid-30s or as late as the mid-50s. It lasts roughly eight to ten years, and one of the earliest signs is cycles that start arriving later than expected or skipping entirely.
During this phase, hormone levels fluctuate unpredictably. You might have a perfectly normal 28-day cycle one month and then wait 40 or 50 days for the next one. Blood tests for FSH (the hormone that stimulates the ovaries) can hint at perimenopause if levels are consistently elevated, but because hormones swing so erratically during this time, a single test can be misleading. The diagnosis is usually based on a pattern of symptoms: changing cycle length, hot flashes, sleep disruption, and mood shifts.
Other Medical Causes
Less common but worth knowing about: conditions that affect the pituitary gland, such as small benign tumors called prolactinomas, can raise prolactin high enough to shut down ovulation. Chronic illnesses like uncontrolled diabetes or celiac disease can also interfere with cycles by creating systemic inflammation or nutrient deficiencies that disrupt hormonal signaling.
Significant acute illness, surgery, or even jet lag across multiple time zones can delay a single period without indicating a deeper problem. If your period is late once and your next cycle arrives on schedule, it was likely a one-time disruption. If periods are repeatedly late or absent for three or more cycles, that pattern points toward something worth evaluating with blood work or imaging.