Why Is My Period Late? Common Causes and When to See a GP

A period is usually considered late when it arrives after your usual cycle pattern, and adult cycles commonly range from 21 to 35 days. Pregnancy is the most common cause to rule out first, but stress, weight change, heavy exercise, hormonal contraception, thyroid problems and perimenopause can also delay a period.

Many people have a late or missed period at some time. The NHS says that most of the time it is nothing to worry about, but that you should see a doctor about a late or missed period just in case. A single late period is not the same as periods stopping altogether, and the right next step depends on your pattern, your age and any other symptoms.

How late is late?

Count a cycle from the first day of one period to the first day of the next. Adult cycles commonly last 21 to 35 days, so a period a few days after you expected it may still be within your normal range — especially if your cycles vary. A period is more clearly a concern when it is missed altogether, when cycles keep getting longer or shorter, or when a change comes with other symptoms.

Mayo Clinic defines amenorrhoea as the lack of a menstrual period, either by never menstruating or by missing three or more periods or cycles. Secondary amenorrhoea means you have had periods in the past but then miss three or more in a row, or have no period for more than six months if your cycles were irregular. That is a useful line: one late period is common, while three missed periods in a row deserve a medical check.

Common causes of a late period

Pregnancy and breastfeeding

Pregnancy is the most common cause of secondary amenorrhoea, according to Mayo Clinic, and it is the first cause to rule out if you could be pregnant — even if your cycles are irregular, because ovulation can still happen. Breastfeeding can also delay the return of periods, as can the approach of menopause.

Stress

The NHS lists stress among the common causes of a late or missed period. Mayo Clinic explains that mental stress can, for a limited time, alter the work of the hypothalamus — the area of the brain that controls the hormones that direct the menstrual cycle — so ovulation and menstruation may stop. Regular periods usually start again if stress levels fall. Severe, long-lasting anxiety is also listed by Mayo Clinic as a risk factor for periods stopping or becoming less frequent.

Weight change and eating too little

Sudden weight loss and being overweight are both listed by the NHS as causes of a late or missed period. Mayo Clinic adds that eating too few calories can suppress the hypothalamus and cause amenorrhoea, and that eating disorders such as anorexia or bulimia raise the risk. If weight, diet or eating habits have changed sharply, that is worth mentioning to your doctor.

Too much exercise

Doing too much exercise is another NHS-listed cause. Mayo Clinic notes that rigorous training, such as ballet or long-distance running, can be linked with amenorrhoea, with low body fat, stress and high energy needs all playing a part. Periods often return when training load and energy intake come back into balance, but a doctor can help you judge whether that is the likely cause.

Hormonal contraception and medicines

Certain hormonal methods of contraception can delay or stop periods, including the contraceptive pill, the contraceptive injection and the intrauterine system (IUS), according to the NHS. Mayo Clinic adds that hormonal implants, some pills, levonorgestrel intrauterine devices and injections can cause amenorrhoea, and that periods may take time to return after stopping — longer after injections. Some other medicines can also stop periods, including certain antipsychotics, cancer chemotherapy, blood pressure medicines and opioids, so tell your doctor about everything you take.

Hormonal conditions

Several hormone-related conditions can delay periods. The NHS lists polyendocrine metabolic ovarian syndrome (PMOS), formerly called polycystic ovary syndrome (PCOS), and notes that periods can also stop because of an overactive or underactive thyroid. Mayo Clinic lists PCOS, thyroid conditions, a noncancerous pituitary tumour and primary ovarian insufficiency — when the ovaries stop working as they should before age 40 — among the hormonal causes of amenorrhoea.

Other signs that can come with a hormonal cause include milky nipple discharge, hot flushes, vaginal dryness, hair loss, headache, vision changes, excess facial hair, pelvic pain and acne, according to Mayo Clinic. You do not need to have any of these for a late period to be worth checking, but they are helpful details to share with your doctor.

Perimenopause

The start of menopause, or perimenopause, usually between the ages of 45 and 55, is listed by the NHS as a common cause of late or missed periods. Cycles often become irregular during this transition before periods stop altogether. If you are in this age range and your cycles are changing, a GP can help you work out whether perimenopause fits the picture.

Other medical conditions

Periods can also stop because of medical conditions such as heart disease, diabetes or thyroid disease, according to the NHS. Cleveland Clinic notes that amenorrhoea is usually the sign of a treatable condition, and that once a provider works out the cause, care to regulate the cycle may involve lifestyle changes or hormonal treatment. Structural conditions, such as uterine scarring after surgery or a blockage in the vagina, are less common causes listed by Mayo Clinic.

What to do when your period is late

Start by checking the basics. Note the first day of your last period, whether your cycles are usually regular, and whether anything has changed recently — stress, weight, exercise, illness, a new medicine or a change in contraception. If you could be pregnant, take a pregnancy test and talk to a doctor or pharmacist if you are unsure about the result or timing.

Do not try to force a period with unproven remedies or by changing prescribed medicines on your own. If a late period is a one-off and your next cycle returns to normal, it may simply have been a variation. Keeping a simple record of your cycles makes it much easier for a doctor to spot a pattern if the problem repeats.

A GP will usually ask about your health and may do blood tests to find the cause, according to the NHS, and may refer you to a gynaecologist or endocrinologist if you need more tests or scans. Treatment depends on the cause — for example, the combined contraceptive pill may help make periods more regular in PMOS, and hormone replacement therapy may be used if you are starting perimenopause. Talk to a doctor or pharmacist before starting, stopping or changing any medicine.

When to see a doctor

See a GP if you have missed your period three times in a row, if your periods have not started by the time you are 15, if you have missed a period and have other symptoms such as weight gain or loss, tiredness, facial hair growth, or dry or oily skin, or if your periods have become irregular. Mayo Clinic gives the same three-missed-periods threshold, and adds that you should seek care if you have never had a period and are 15 or older.

Get urgent medical help the same day if a late or missed period comes with severe or one-sided pelvic pain, shoulder-tip pain, fainting, very heavy bleeding, or a positive pregnancy test with pain or bleeding, as these can signal a pregnancy outside the womb (ectopic pregnancy) or another emergency.

In an emergency call 911 (US), 999 (UK) or 112 (EU).