What counts as irregular periods?

What are irregular periods?

Irregular periods are cycles outside the expected range, that vary a lot from one month to the next, or that stop for a stretch. The expected range is wider in the first few years after periods begin.

ACOG's guidance on menstruation in girls and adolescents treats the following as normal early on: cycles of 21–45 days, bleeding for 2–7 days, cramps on the first day or two that ease with ibuprofen or a hot water bottle, and some mood changes or bloating beforehand.

When periods stop altogether, doctors use the word amenorrhea. "Hormonal imbalance" is a broad label, and it is worth asking which cause is meant, because the ones below can each be checked.

What can irregular periods mean?

Irregular periods have several well-described causes, and the pattern of your cycles gives a provider or GP something to work from. The US Office on Women's Health lists PCOS and perimenopause among them.

PCOS is one. WHO estimates that it affects 10–13% of women of reproductive age and that up to 70% are undiagnosed, so it is common and often goes unrecognized. Acne with excess hair growth alongside irregular cycles is worth mentioning. UK readers may see the NHS name polyendocrine metabolic ovarian syndrome (PMOS).

Perimenopause is another, and irregular periods in perimenopause follow a recognizable sequence. The STRAW+10 staging system (Harlow et al., 2012) marks the early transition by a persistent difference of 7 days or more between consecutive cycles, and the late transition by 60 days or longer without a period. The NHS says symptoms usually last 7–9 years, and pregnancy is still possible.

For periods that stop sooner than expected, our page on early menopause is for that situation.

For girls and women who train hard, RED-S, short for Relative Energy Deficiency in Sport, belongs on the list. The IOC consensus statement (Mountjoy et al., 2023) names lost or irregular periods, frequent injuries, stress fractures and low mood as warning signs, and notes that it harms bone at the age bone should be building fastest. The same statement is clear that periods should never be seen as a normal casualty of training, so a missing one is worth raising.

How late is too late, and how often is too often?

For adults, US guidance suggests calling a provider after about 90 days with no period when you are not pregnant or breastfeeding; the NHS gives no day count and advises a GP visit for any irregular periods. Too often means cycles that keep coming in under the lower limits above.

Teenagers have more room. Cycles longer than 38 days are common for a few years after the first period, and they usually become more regular within three years. Periods more than 3 months apart once settled are worth a doctor's visit.

A first period that has not started by age 15 is worth checking, as is one that begins before age 8; our page on early puberty is for families in that situation.

Heaviness and pain count as much as timing. Reasons to see a doctor include soaking a pad or tampon every 1–2 hours, bleeding for longer than 7 days, clots bigger than a quarter, and pain that stops school or does not ease with painkillers. In the UK the first appointment is with a GP.

What the guidance does and does not show

The US and UK definitions answer different questions. The Office on Women's Health describes where typical adult cycles fall, while the NHS sets the point at which a cycle counts as irregular, so a cycle can be typical on one and irregular on the other. Neither is more correct. If your cycle sits between the two, a lasting change from your own usual pattern is the useful thing to bring to an appointment. The ACOG range for the early years works the same way: it shows where typical cycles fall, so a cycle near its edge is not automatically a problem.

STRAW+10 is a staging system. It describes the order in which cycle changes tend to arrive, not a date for the final period. The WHO figures for PCOS are estimates of how common it is, not a way of telling who has it. The IOC statement is an expert consensus that names warning signs to raise, not a diagnosis in itself.

Next steps

A good place to start is a period diary. For a few months, note cycle length, heaviness, pain and mood, so that an appointment with a provider, or a GP in the UK, begins with evidence instead of memory. It is worth booking that appointment when cycles stay outside the ranges on this page or when any of the signs above apply. If you are in your 40s and your cycles are changing, contraception is worth raising in the same visit. These ranges are guides drawn from large groups of women, and your age, training and health history all shape what is usual for you, so what fits is yours to decide with your provider: periods are not one size fits all.