Irregular periods in your 20s: when it is normal and when to see a GP
According to the NHS, your cycle is irregular when the gap between two periods is under 21 or over 35 days. The most common causes are stress, a change in weight, excessive exercise and hormonal contraception, and less often – polycystic ovary syndrome or a thyroid problem. You need to be seen if your usual pattern changes, a period lasts more than 7 days, you bleed between periods or you are struggling to get pregnant.
- A normal cycle is around 28 days on average; it is irregular if under 21 or over 35 days (NHS).
- Stress, weight, exercise and hormonal contraception are the most common causes.
- After stopping progestogen-only contraception your periods should return; if you miss more than three periods and are not pregnant – see a doctor (nidirect).
- Bleeding between periods is always a reason to see a doctor.
What does "irregular periods" mean?
According to the NHS, the average gap between two periods is around 28 days, but shorter and longer cycles are common. A cycle is considered irregular when the gap is under 21 or over 35 days. Day 1 is the first day of your period, and the last day of the cycle is the day before the next one. An irregular cycle in itself is not a sign of a problem, but a change in your usual pattern deserves attention.
What are the most common causes of irregular periods?
The NHS lists as common causes: puberty and the approach of the menopause (usually between 45 and 55), pregnancy – a missed period is often its first sign, hormonal contraception (especially the progestogen-only pill, the injection and the hormonal coil), significant weight loss or gain, stress and anxiety, and excessive exercise.
Less often the cause is polycystic ovary syndrome or thyroid problems – conditions that are diagnosed with an examination and tests.
What happens to your cycle after stopping hormonal contraception?
Some methods – the progestogen-only pill, the injection and the hormonal coil – can stop your periods completely. According to information from the Northern Ireland health service (nidirect), after stopping them your periods should return. If you are not pregnant and miss more than three periods in a row, that is a reason to be seen.
When should you see a doctor?
The NHS recommends seeing a GP or gynaecologist if:
- your periods are irregular or your usual pattern has changed;
- a period lasts more than 7 days;
- the irregular periods come with other symptoms – weight gain, tiredness, facial hair, dry or oily skin;
- you have bleeding between periods;
- your periods are irregular and you are struggling to get pregnant.
nidirect adds: more than three periods in a row missed without pregnancy, and periods stopping before the age of 45.
What can you expect at the appointment?
Treatment is not always necessary. The doctor may refer you to a gynaecologist or endocrinologist and order blood tests for hormones or an imaging scan to find the cause. If there is one, treatment depends on it.
What helps in the meantime?
The NHS explicitly recommends keeping a diary or using a period-tracking app. After a few cycles you can see whether there is a pattern and what it is, and your doctor gets specific data instead of rough memories.
Frequently asked questions
How many days late is normal?
The NHS does not give an "allowed delay", but limits for the whole cycle: between 21 and 35 days is considered regular. A one-off deviation with stress or travel is common; a repeated deviation outside these limits is a reason to be seen.
Can stress alone shift your cycle?
Yes. The NHS lists stress and anxiety among the common causes of irregular periods, alongside changes in weight and excessive exercise.
Do irregular periods make it harder to get pregnant?
They can, because ovulation is less predictable. The NHS recommends seeing a doctor if your periods are irregular and you are struggling to get pregnant – there are tests and treatment depending on the cause.
Sources
- NHS – Irregular periods – last reviewed by the NHS: 26 June 2026
- nidirect (NHS Северна Ирландия) – Stopped or missed periods – adapted from the NHS
Informational article retold in our own words from the sources listed. It does not replace a consultation with a doctor; in an emergency call 112. If you spot an inaccuracy, write to [email protected].