Lo básico del ciclo

What counts as a normal cycle

Revisado: 4 de octubre de 2026

Solo en inglés por ahora

Most adult cycles last between about 21 and 38 days, and periods last 2 to 7 days. Some change from month to month is normal. Here is what to expect and when to get checked.

Normal ranges for adults

Your cycle length is counted from the first day of one period up to the day before the next one starts. Health bodies give slightly different normal ranges. The US Office on Women's Health says 24 to 38 days, and the NHS says 21 to 35 days. Put together, most adult cycles last somewhere between about 21 and 38 days. The average is around 28 days, but few people have exactly 28 days every time.

Some change is normal

Your cycle does not need to be the same length every month. It varies between people, and from month to month in the same person. Your periods still count as regular if they usually come within the normal range. Logging your period dates in Ciclo for a few months shows you your own usual range, which tells you more than comparing yourself with an average.

How long periods last

A period usually lasts 2 to 7 days, most often about 5. Over a whole period, most people lose about 20 to 90 ml of blood, roughly 1 to 5 tablespoons, although some bleed more heavily. Get checked if bleeding lasts more than 7 days. Also get checked if you need a new pad or tampon every 1 to 2 hours.

How cycles change with age

For a few years after periods start, cycles longer than 38 days are common. They usually become more regular within about 3 years. If they are still long or irregular after that, see a doctor or nurse. In your 20s and 30s, cycles tend to be regular. In your 40s, as the body starts moving towards menopause (perimenopause), cycles may become irregular again. Periods stop at menopause, usually in the mid-40s to mid-50s.

What can change your cycle

Periods stop in pregnancy, and if you breastfeed, they can take a while to come back. Long-term stress can make periods irregular. Gaining or losing a lot of weight can make you miss periods, and very low body fat can stop ovulation. Health conditions such as thyroid problems and polycystic ovary syndrome (PCOS) can affect your cycle, and so can some medicines, including some for epilepsy or anxiety. Hormonal contraception and exercising very hard can also change your periods.

When to see a doctor or nurse

Talk to a doctor or nurse if your cycles are regularly shorter than 24 days or longer than 38 days, or if regular periods become irregular. Also talk to one if you have no period for 3 months and are not pregnant or breastfeeding. Bleeding between periods or after sex should be checked too. Get urgent help if you are bleeding very heavily and feel dizzy, faint or very weak.

This is general information. Your own normal may differ from the average; if your cycle changes or worries you, talk to a doctor or nurse.