Periodos

Irregular periods

Revisado: 4 de octubre de 2026

Solo en inglés por ahora

It is normal for your cycle to vary a little. Learn what can make periods irregular, when it is expected, and when it is worth talking to a doctor or nurse.

What irregular means

Your cycle is the time from the first day of one period to the first day of the next. Most adult cycles last somewhere between about 21 and 38 days, and a cycle can be a bit shorter or longer from one month to the next. Periods are called irregular when the gap between them keeps changing, or is often shorter than 24 days or longer than 38 days. Sometimes a period is missed altogether.

Times when it is expected

Irregular periods are normal for the first few years after periods start. During this time, cycles longer than 38 days are common. They are also normal in the years leading up to menopause. Menopause usually happens between the mid-40s and mid-50s. Pregnancy stops periods, so a missed period is often an early sign of pregnancy. Some hormonal contraception, such as the progestogen-only pill, the contraceptive injection and the hormonal IUD (coil), can also make bleeding irregular.

Other common causes

Stress and anxiety, losing or gaining a lot of weight, and exercising very hard can all affect your cycle. Eating disorders can also disrupt periods. Health conditions that can cause irregular periods include polycystic ovary syndrome (PCOS, now also called PMOS), thyroid problems, high levels of the hormone prolactin, diabetes that is not well controlled, and pelvic inflammatory disease. Another cause is premature ovarian insufficiency (POI), when the ovaries stop working normally before age 40. Some medicines can also play a part.

Finding the cause

Irregular periods do not always need treatment. A doctor or nurse will ask about your periods and any other symptoms. They may arrange tests or refer you to a specialist to find the cause. Treatment depends on what is behind it. It might mean treating a condition such as a thyroid problem, or using hormonal contraception. Logging your period dates in Ciclo makes the pattern easier to show, though its predictions are less certain when your cycles vary.

When to see a doctor or nurse

Talk to a doctor or nurse if your cycles are often shorter than 24 days or longer than 38 days, if your periods were regular and have become irregular, or if a period lasts more than 7 days. Also get checked if you have had no period for 3 months and are not pregnant or breastfeeding. The same applies if you bleed between periods, or if you are trying to get pregnant and it is not happening. Irregular periods together with weight gain, tiredness, extra hair on your face, or dry or oily skin are also worth checking. If you might be pregnant and have pain low down on one side of your tummy, get medical help the same day.

This is general information, not a diagnosis. If your cycle changes or worries you, talk to a doctor or nurse.