A period can be “late” for many reasons, and the answer depends a lot on where you are in life. If you’re a teenager who hasn’t gotten a first period yet, you’re likely still within the normal window. The median age for a first period is about 12.4 years, but any time up to age 15 is considered typical. By age 15, roughly 98% of girls will have started menstruating. If you’ve already been having periods and one hasn’t shown up on schedule, the most common culprits are stress, hormonal shifts, changes in weight or exercise, and certain medications.
If You’re Waiting for Your First Period
A first period (called menarche) typically arrives between ages 12 and 13 in well-nourished populations, but the range is wide. Some girls start as early as 9 or 10, while others don’t begin until 14 or 15. Breast development is usually the earliest visible sign of puberty, and periods tend to follow within two to three years. If you’ve noticed breast changes, body hair, or growth spurts, your body is progressing through puberty and a period will likely follow.
The American College of Obstetricians and Gynecologists recommends an evaluation if a first period hasn’t arrived by age 15, or if it hasn’t started within three years of breast development beginning. A lack of any breast development by age 13 is also worth looking into. In these cases, the delay can sometimes trace back to genetic conditions, differences in how reproductive organs developed, or hormonal signals that aren’t firing correctly between the brain and the ovaries.
Stress and Energy Balance
Your brain acts as a gatekeeper for your menstrual cycle. A region called the hypothalamus sends signals that ultimately trigger ovulation. When your body is under significant stress, whether emotional, physical, or nutritional, those signals can slow down or stop entirely. This is one of the most common reasons for a missed period outside of pregnancy.
Caloric intake plays a particularly important role. Not eating enough to match your energy output can disrupt your cycle even without intense exercise. Research has shown that some athletes who develop irregular periods are simply not consuming enough calories to support both their training and their reproductive system. An older but influential hypothesis suggested that body fat needs to reach about 17% for periods to begin and about 22% for them to resume after being lost, though later studies found plenty of women menstruating normally below those thresholds. The takeaway is that there’s no single magic number for body fat. What matters more is whether your body perceives an energy shortage.
Rapid weight loss, restrictive eating patterns, and very high training volumes can all push the body into that energy-deficit zone. If your period disappears alongside significant changes in diet or exercise, that connection is worth paying attention to.
Polycystic Ovary Syndrome (PCOS)
PCOS is one of the most common hormonal conditions in women of reproductive age, and irregular or missing periods are a hallmark symptom. It’s diagnosed when someone has at least two of the following three features: higher-than-expected levels of androgens (sometimes called “male hormones,” though everyone produces them), irregular ovulation, and a characteristic appearance of the ovaries on ultrasound.
In practice, PCOS often shows up as cycles that are longer than 35 days, fewer than eight periods a year, or stretches of 90 days or more without a period. Other signs include acne that doesn’t respond well to typical treatments, thinning hair on the scalp, and excess hair growth on the face or body. If those symptoms sound familiar, it’s a pattern worth investigating, since PCOS is manageable but does benefit from early identification.
Thyroid Problems
Your thyroid gland, which sits at the front of your neck, produces hormones that influence nearly every system in your body, including your reproductive cycle. Both an underactive thyroid (hypothyroidism) and an overactive one (hyperthyroidism) can cause periods to become irregular, lighter, heavier, or disappear altogether.
The connection works through a chain reaction. When thyroid hormone levels are off, they alter levels of other hormones involved in ovulation, including prolactin, a hormone best known for triggering milk production. Elevated prolactin can suppress the signals that tell your ovaries to release an egg, which in turn delays or prevents a period. Thyroid issues are straightforward to detect with a blood test and are one of the first things checked when periods go missing.
Medications That Can Stop Periods
A surprisingly long list of medications can interfere with your cycle. Many work by raising prolactin levels, which suppresses ovulation. Others shift the balance between estrogen and androgens. Common categories include:
- Antipsychotics and mood stabilizers: Several widely prescribed psychiatric medications are known to cause missed periods.
- Antidepressants: SSRIs, tricyclics, and MAO inhibitors can all affect menstrual regularity.
- Opioid pain medications: Both prescription opioids and illicit drugs like cocaine can stop periods.
- Anti-seizure medications: Certain drugs used for epilepsy are linked to cycle disruption.
- Some blood pressure medications and digestive drugs: These can also raise prolactin as a side effect.
If your period disappeared around the time you started a new medication, that’s a connection worth raising with whoever prescribed it. Stopping or switching medication can often restore normal cycles, but don’t make changes on your own.
After Stopping Birth Control
If you recently came off hormonal contraception, a delay is normal. Most people see their cycle return within one to three months after stopping the pill, whether it’s a combination pill or a progestin-only version. The process tends to be quick for implants and hormonal IUDs as well.
The notable exception is the injectable shot (Depo-Provera). After stopping those injections, it takes an average of seven to ten months before ovulation resumes. Some people wait even longer. This is well-documented and not a sign that anything is wrong, just a reflection of how long the medication stays active in your system.
After Pregnancy and During Breastfeeding
If you’ve recently had a baby, the timeline for your period’s return depends heavily on how you’re feeding. Formula feeding typically means periods return within a few months of delivery. Breastfeeding can delay your period for many months, and in some cases over a year, especially if you’re nursing frequently and exclusively. This happens because the hormones involved in milk production actively suppress ovulation. As you gradually reduce breastfeeding sessions, your cycle will typically restart.
Perimenopause
If you’re in your 40s (or sometimes late 30s), irregular periods may signal the transition toward menopause. Perimenopause often begins with subtle shifts: your cycle might shorten or lengthen by a week compared to what’s been normal for you. That inconsistency in cycle length, specifically a shift of seven or more days from your usual pattern, is a hallmark of early perimenopause. Later in the transition, gaps of 60 days or more between periods become common. This phase can last several years before periods stop completely.
When a Missed Period Needs Investigation
A single late period is rarely cause for alarm. Cycles naturally vary by a few days, and occasional longer gaps happen to almost everyone. The clinical threshold for concern is three consecutive missed periods if your cycles were previously regular, or six months without a period if your cycles have always been irregular. At that point, the standard workup typically includes a pregnancy test, blood tests checking thyroid function and prolactin levels, and an assessment for PCOS. These are simple, routine tests that can quickly narrow down the cause and point toward a solution.