Cycle length calculator
Cycle length and regularity calculator
Enter the first day of at least three periods to see your average cycle, how much it varies and what that means.
Updated
In short
How do I know if my cycle is regular?
Write down the first day of each period and count the days between them. Doctors use the FIGO guide: a typical cycle is 24 to 38 days, and it's regular if the gap between your shortest and longest cycle is 7 days or less, or up to 9 days if you're 18 to 25 or 42 to 45.
Your cycles
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This is an estimate, not a diagnosis or birth control.
General information, not medical advice. Your doctor or midwife can tell you what your own results mean.
How it's calculated
- Cycle length = days from the first day of one period to the first day of the next.
- Average = the mean of your cycle lengths. Variation = longest cycle − shortest cycle.
- Typical length 24–38 days; regular if the variation is 7 days or less (9 days at ages 18–25 and 42–45), from FIGO 2018.
- More dates give a truer picture. Doctors usually look at a year of cycles.
Gyne learns your real cycle and adjusts these estimates as you log.
Frequently asked questions
Is a 40-day cycle normal?
It's longer than the typical 24 to 38 days. An occasional long cycle can happen, but if your cycles are often longer than 38 days, ask your doctor. Conditions like PCOS and thyroid problems can lengthen cycles.
Are cycles more irregular at some ages?
Yes. Cycles are often irregular in the first years after periods start and in the years before menopause, which is why the regular range is a little wider for ages 18 to 25 and 42 to 45.
How many periods should I enter?
At least three, which gives two cycles. Six or more gives a much clearer answer, and a year of dates is what doctors usually use.
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