How many days between periods is normal?
For adults, a normal gap is 21 to 35 days, counted from the first day of one period to the first day of the next. The average is about 28 to 29 days. Teens can have 21 to 45 days. Varying by a few days each month is normal; varying by more than 7 to 9 days, or gaps outside that range, is worth checking.
How to count days between periods
Doctors count from the first day of one period to the first day of the next, not from the end of bleeding. That number is your cycle length. If your last period started on 2 May and the one before started on 4 April, your cycle was 28 days.
If you count from the end of one period to the start of the next, you'll get a smaller number, usually about 3 to 3陆 weeks. That gap is fine too; it just isn't what doctors mean by cycle length.
What's normal at each stage of life
| Stage | Normal cycle length | Notes |
|---|---|---|
| Teens (first few years) | 21 to 45 days | Irregular is common while cycles settle |
| Adults | 21 to 35 days | Average about 28 to 29 days |
| 40s (perimenopause) | Often shorter, then longer | Gaps of 60+ days become more common near menopause |
| On hormonal birth control | Set by the method | Pill bleeds are withdrawal bleeds, not true periods |
A large study of more than 600,000 cycles found an average of about 29 days, and only around 13% of cycles were exactly 28 days. So 28 is a convenient average, not a target. Our cycle length calculator works out your average and range from your dates.
When the gap isn't normal
- Shorter than 21 days regularly: see period every 2 weeks and is a 21-day cycle normal.
- Longer than 35 days regularly: see is a 35-day cycle normal and long menstrual cycle.
- Varying by more than 7 to 9 days between your shortest and longest cycles: see irregular periods.
- No period for 3 months or more (and not pregnant).
Most of the variation in cycle length happens before ovulation. So when your cycle runs long, your PMS days shift later too. Tracking both helps you see harder days coming.
See a doctor if your cycles are regularly shorter than 21 or longer than 35 days, if they change suddenly and stay changed, if your period stops for 3 months, or if you bleed between periods or after sex.
Frequently asked questions
Is 2 weeks between periods normal?
Two weeks from the end of one period to the start of the next can be normal. Two weeks from start to start is too short and worth checking.
Is 40 days between periods normal?
It's longer than the usual adult range. Once in a while it can happen; regularly, it's worth a check. See is a 40-day cycle normal.
Do I count from the start or end of my period?
From the start. Day 1 is the first day of real flow.
How much can my cycle vary and still be normal?
A few days either way is normal. A difference of more than 7 to 9 days between your shortest and longest cycles is considered irregular.
Sources
- NHS: Periods
- ACOG: Your First Period
- Bull JR et al. Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. npj Digital Medicine (2019)
- NHS: Irregular periods
This page is for information only and isn鈥檛 medical advice. If something worries you, please talk to a doctor.
Keep reading
Cycle length calculator: is my cycle normal?Free cycle length calculator: enter the start dates of your last few periods to get your average cycle length and see whether your cycle counts as regular.
How long is a normal menstrual cycle?How long is a normal menstrual cycle? Anywhere from 21 to 35 days in adults. What's average, how much variation is fine, and when to see a doctor.
Irregular periods: what counts, common causes and what helpsIrregular periods explained: what counts as irregular, why cycles vary, common causes like PCOS, thyroid and perimenopause, and when to see a doctor.Is a 35-day cycle normal?Is a 35 day cycle normal? Yes, it's at the long end of the 21 to 35 day adult range. When you ovulate, common causes of long cycles, and when to check.The 4 phases of the menstrual cycle, in colorThe 4 phases of the menstrual cycle explained simply: what your hormones do in each, how long each lasts, and how mood and energy usually change.