Why is my period late?

Late periods have many causes and are usually nothing to worry about, but see a doctor just in case (NHS). Common causes include pregnancy and stress (NHS), and most home tests work from the first day of a missed period (NHS). See a doctor after 3 missed periods in a row (NHS), and get help quickly for the warning signs.

By Hossam Hamouda, developer of Period Calc · Last updated: 25 October 2026

Predictions are estimates, not medical advice or a diagnosis, and not a method of contraception.

How late is a late period?

The NHS and ACOG pages used here do not say after how many days a period counts as late. The NHS is the UK health service, and ACOG is the American College of Obstetricians and Gynecologists. The NHS says many women have a missed or late period at some time. It says this is usually nothing to worry about, but that you should see a doctor about it just in case (NHS).

Count from the first day of your last period, as explained in how long a period and a cycle last. Or let the period calculator show the date you expected.

Common reasons for a late period

If you have had sex, pregnancy comes first: you could be pregnant if you miss a period (NHS). A bleed like a very light period around the time your period is due can be implantation bleeding, an early sign of pregnancy (NHS).

These are common causes the NHS lists for a missed or late period (NHS):

• stress;
• sudden weight loss, or being overweight;
• too much exercise;
• some hormonal contraception, such as the pill, the injection or an IUS (a hormone device in the womb);
• breastfeeding;
• the start of the menopause, called perimenopause, usually between the ages of 45 and 55 (the menopause is the time when periods stop for good, says ACOG);
• polycystic ovary syndrome (PCOS), which the NHS now calls polyendocrine metabolic ovarian syndrome (PMOS); ACOG describes it as a condition that leads to a hormone imbalance affecting periods and ovulation (ACOG);
• medical conditions such as heart disease, diabetes or thyroid problems.

ACOG’s list of reasons adds eating disorders and low body weight (ACOG). The NHS says changing your method of contraception can also upset your cycle (NHS). A doctor can look for the cause, and treatment depends on it (NHS).

When to take a pregnancy test

Most home pregnancy tests work from the first day of a missed period (NHS). The pregnancy test date calculator shows the date your next period is due.

My period is late and the test is negative: what now?

A negative result is less reliable than a positive one, for example if you test too early or do not follow the instructions (NHS). If your test is negative and you still think you are pregnant, wait a few days and test again. If a second test is negative and your period has still not come, see a doctor (NHS). The NHS also says to see a doctor if a pregnancy test is negative and you have missed 3 periods in a row (NHS).

When to see a doctor

• You have missed 3 periods in a row (NHS), or your period has stopped for about 3 months and you cannot explain why (ACOG).
• A second pregnancy test is negative and your period has still not come (NHS).
• Your periods have not started by age 15 (NHS, ACOG).
• You have missed a period and also have weight gain or loss, tiredness, hair growth on your face, or dry or oily skin (NHS).
• Your periods have become irregular (NHS): see irregular periods.

ACOG says that missing periods can be a sign of an underlying medical issue (ACOG).

Warning signs that need help quickly

Get medical help quickly if you have all of these (NHS):

• you have recently missed a period;
• you have unusual vaginal bleeding;
• you have pain anywhere in your tummy, including your lower tummy (pelvic pain).

The NHS says this could be an ectopic pregnancy (a pregnancy growing outside the womb) and needs to be checked as soon as possible (NHS).

In the UK, the NHS says to call 999 or go to A&E (accident and emergency) immediately if you have a combination of these signs (NHS):

• a sharp, sudden and intense pain in your tummy;
• feeling very dizzy or fainting;
• feeling sick;
• looking very pale.

The NHS says these signs could mean that a fallopian tube (a tube that connects an ovary to the womb) has split open. This is very serious, but treatable if dealt with quickly (NHS). Outside the UK, use your local emergency number. ACOG says to go to an emergency room for sudden, severe pain in your tummy or pelvis (your lower tummy), shoulder pain, or weakness (ACOG).

Getting ready for the visit

Write down the first day of your last few periods and any other symptoms. The NHS says a diary gives your doctor a detailed idea of what happens and when (NHS).