Cycle length calculator
Enter the start dates of your last periods, from 2 to 6, to get your average cycle length.
Enter at least two different start dates.
Cycle length is the number of days from the first day of one period to the first day of the next.
Your dates never leave this page. Everything is calculated in your browser, and nothing is saved or tracked.
Estimates only. Not a method of contraception. Not medical advice.
Frequently asked questions
- How is cycle length measured?
- It is the number of days from the first day of one period to the first day of the next.
- How many dates should I enter?
- Two dates give one cycle. More dates, up to six, give a steadier average.
- What does irregular mean here?
- If your longest and shortest cycles differ by more than 7 days, the tool shows a note that your cycles vary. It is a label for this calculator, not a diagnosis.
- What can I do with the result?
- Use your average in the ovulation calculator or the period calculator for better estimates.
- Do you save my dates?
- No. Everything stays on this page and nothing is stored or sent.