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What is a normal cycle length?
A normal menstrual cycle is 21 to 35 days long, counted from the first day of one period to the day before the next (NHS). Only about 13% of cycles are exactly 28 days. Varying by a few days each month is normal; regularly shorter than 21 or longer than 35 days is worth mentioning to a GP.
- Normal cycle length: 21 to 35 days (NHS). FIGO allows 24 to 38. The average is around 28 to 29.
- Periods usually last 2 to 7 days.
- Small month-to-month changes are normal, especially in your teens and as you near menopause.
- Your own pattern over several cycles is the best guide.
Key facts
- Normal range: 21 to 35 days (NHS).
- Average cycle length was about 29 days across 600,000+ cycles, and only around 13% were exactly 28 days (Bull et al., 2019).
- Gynaecologists’ FIGO system calls cycles under 24 days “frequent” and over 38 days “infrequent”.
If your cycle is not 28 days, welcome to the majority. The NHS says a cycle typically comes around every 28 days, but anything from 21 to 35 days is normal. Your period itself lasts 2 to 7 days, usually about 5.
Different experts, slightly different lines
There is no single magic number. The NHS and WHO use 21 to 35 days. The international gynaecology federation (FIGO) uses a slightly wider 24 to 38 days, and says the gap between your shortest and longest cycle should be up to about 7 to 9 days, with periods of up to 8 days. For teenagers, the American College of Obstetricians and Gynecologists says 21 to 45 days is normal. Either way, the picture is the same: a wide healthy range.
What counts as a regular cycle?
Regular does not mean identical. A few days of wobble from month to month is normal. It is the overall pattern over several cycles that matters, which is why logging a few months is so helpful.
What changes cycle length?
- Age: cycles tend to be longer and less predictable in the first few years after periods start. In the app study, average cycle length got a little shorter with age in adulthood, then changes again in perimenopause.
- Hormonal contraception: pills, implants, injections and hormonal coils change bleeding patterns, and what looks like a period may be a withdrawal bleed.
- Life: stress, illness, travel, sleep, and big changes in eating, weight or exercise.
- After pregnancy or while breastfeeding.
MythA 32-day cycle means something is wrong.
The NHS gives 21 to 35 days as the normal range, so 32 days is well inside it. What matters more is whether your cycle is steady for you and how you feel.
Questions people ask
Is a 35-day cycle normal?
Yes. The NHS gives 21 to 35 days as the normal range. What matters more is whether your cycle is usually about the same length for you.
How do I work out my cycle length?
Count from day 1 of one period (the first day of proper bleeding) to the day before the next period starts. Averaging three to six cycles gives a better picture than one.
Sources
Written by the Splash teamSources checked
This is general information, not medical advice. Splash can’t diagnose. If you’re worried, talk to a GP, pharmacist or sexual health clinic. In an emergency call 999 (UK) or 911 (US). How we write and check articles.