Why Is My Period Late? How Many Days Is Normal and When to Take a Test

In brief:

• It is normal for a period to come every 21 to 35 days; if the gap is longer than 35 days, periods are considered irregular (NHS).
• Most pregnancy tests are reliable from the first day your period is late. If you do not know when your period is due, take the test at least 21 days after unprotected sex (NHS).
• If the test is negative but your period has not come, repeat it a few days later. If the second test is also negative, see a doctor (NHS).
• The NHS and MedlinePlus do not recommend herbs for a late period; what to do depends on the cause of the delay. Pennyroyal oil, promoted as a way to "bring on a period", is poisonous when taken by mouth (NIH LiverTox).
• If you have missed 3 periods in a row, see a doctor (NHS).

How many days late is normal?

According to the NHS, most women get a period about every 28 days, but any gap between 21 and 35 days is normal. If the time between two periods is shorter than 21 days or longer than 35 days, periods are considered irregular. The gap can also change from month to month; a period sometimes comes early and sometimes late.

So if your usual cycle is 28 days and your period is a few days late, the gap may still be within normal limits. According to the NHS, a late period is often nothing to worry about, but it is still worth looking at the cause.

To measure the delay accurately, note your periods in a calendar or an app. The first day of your cycle is the day your period starts; the last day is the day before your next period (NHS). Cycles become irregular more often in the first years of having periods and as you approach menopause (NHS).

If your periods have been irregular for a long time, that is different from a single late period. We explain it in When and Why Do Irregular Periods Happen?.

What causes a late period?

Common causes listed by the NHS and MedlinePlus:

• Pregnancy: the most common reason for a late period (MedlinePlus).
• Stress and severe anxiety (NHS, MedlinePlus)
• Sudden weight loss or excess weight: this includes strict diets and rapid weight loss after stomach surgery (MedlinePlus).
• Too much exercise (NHS)
• Breastfeeding (NHS)
• Hormonal contraception: the NHS lists the contraceptive pill, the contraceptive injection and the hormonal intrauterine system among the reasons periods may be late or stop. According to MedlinePlus, it can take more than 6 months for periods to return after stopping the pill or the injection.
• Perimenopause: the transition to menopause usually starts between 45 and 55 (NHS). More in What Is Perimenopause?.
• PMOS (formerly PCOS): the NHS now uses the condition's new name, "polyendocrine metabolic ovarian syndrome".
• Thyroid problems: both an overactive and an underactive thyroid can affect periods (NHS).

Less common causes include diabetes and heart disease (NHS), pituitary gland tumours, some psychiatric and cancer medicines, early ovarian failure and adrenal gland disorders (MedlinePlus).

If you have taken the morning-after pill, we explain when your next period may come in The Morning-After Pill: Everything You Need to Know.

When should you take a pregnancy test?

According to the NHS:

• Most pregnancy tests can be used from the first day your period is late.
• If you do not know when your period is due, take the test at least 21 days after unprotected sex.
• Some very sensitive tests can be used even before your period is late.
• You can use urine from any time of day; it does not have to be first-morning urine.
• Taking the contraceptive pill does not affect the result. No method protects you one hundred per cent, so if in doubt, take a test.

Tests measure the hormone hCG, which starts being produced about 6 days after fertilisation (NHS). Home tests are reliable if you follow the instructions on the box. A positive result is almost always correct. A negative result is less reliable: it can be misleading if the test was done too early or the instructions were not followed. Some medicines can also affect the result (NHS).

If you get a negative result but still think you may be pregnant, wait a few days and repeat the test. If the second test is also negative and your period still has not come, see a doctor (NHS).

Do herbs that "bring on a period" work?

There are two things to know about teas, oils and herbal mixtures promoted as a way to "bring on a period".

First: the NHS and MedlinePlus do not recommend herbs for a late period. Both say that what to do depends on the cause of the delay. Whether the cause is pregnancy, stress, a change in weight or a thyroid problem, the approach changes accordingly.

Second: some of the herbs mentioned for this purpose are poisonous. According to LiverTox, the liver injury database of the US National Institutes of Health, pennyroyal (Mentha pulegium) oil:

• was used in the past to bring on periods and to cause abortion;
• is highly toxic when taken by mouth;
• even in amounts as small as a tablespoon (15 mL) can cause fainting, seizures, coma, liver and kidney damage and failure of several organs;
• is not recommended for internal use.

If there is a chance you are pregnant, take a pregnancy test first instead of trying to start bleeding. If you are thinking of using a herb or product, ask your pharmacist or doctor first.

What does a doctor do?

According to the NHS, a doctor will ask about your health and may order blood tests to find the cause. If needed, they will refer you to a gynaecologist or a hormone specialist.

According to MedlinePlus, a pregnancy test is done first. The doctor may also order:

• hormone tests such as FSH, LH, prolactin, testosterone, oestradiol and TSH (thyroid);
• a pelvic ultrasound.

What is done depends on the cause. As examples, the NHS mentions the combined contraceptive pill, which helps regulate periods in PMOS, and hormone therapy in perimenopause. A doctor may also offer support to reduce stress and maintain a healthy weight (NHS).

When should you see a doctor?

According to the NHS, see a doctor if:

• You have missed 3 periods in a row
• You are 15 and your periods have not started
• Your period is late and you also have changes such as weight gain or loss, tiredness, facial hair, or dry or oily skin
• Your periods have become irregular
• Two pregnancy tests are negative but your period has not come

MedlinePlus advises acting earlier: see a doctor or gynaecologist when you miss more than one period.

Go to A&E straight away: if there is a chance you are pregnant and you have sudden, sharp and severe pain in your tummy together with dizziness, fainting, nausea or looking very pale, go to the emergency department without waiting. According to the NHS, these can be signs that the tube has burst in an ectopic pregnancy; it is an emergency. Even if your pregnancy test has not been positive, if your period is late and several of these signs appear together, seek medical help immediately (NHS): pain low down on one side of your tummy, vaginal bleeding or a brown watery discharge, pain in the tip of your shoulder, and discomfort when peeing or pooing.

Frequently asked

How many days can stress delay a period?

The sources do not give a set number of days. The NHS lists stress among the common causes of a late period; a doctor can offer advice or support to reduce stress. If the delay lasts longer or keeps happening, the cause should be looked into.

My pregnancy test is negative but my period has not come. What should I do?

According to the NHS, the result can be misleading if the test was done too early. Wait a few days and repeat the test. If the second test is also negative and your period still has not come, see a doctor. If the gap between your periods is often longer than 35 days, tell your doctor (NHS).

Is my period late after stopping the pill?

It can be. According to MedlinePlus, it can take more than 6 months for periods to return after stopping the contraceptive pill or a hormone injection. You can also get pregnant during this time; if in doubt, take a test.

Is it safe to drink herbal teas to bring on a period?

The NHS and MedlinePlus do not recommend herbs for a late period. Some herbal products, such as pennyroyal oil, can cause serious poisoning when taken by mouth (NIH LiverTox). Take a pregnancy test first; if you are thinking of using a product, ask your pharmacist or doctor.