Understand your pattern · Free planning tool

Menstrual cycle-length calculator

Count the days between consecutive period starts. Bring the results to a consultation, or use them to understand your own recent pattern.

An educational planning aid, not a diagnosis or treatment recommendation.

Your dates, a clearer picture

Enter 2–4 consecutive period start dates, oldest first. Leave unused dates at the end blank.

Your entries are calculated in this page and are not submitted to ProFertility or saved to your patient record by this tool. Clear the form when using a shared device. These tools provide educational estimates, not medical advice.

How this is calculated

Each cycle length is the number of calendar days between one period start date and the next. The average, shortest and longest are calculated only from the dates you enter. This describes recorded cycles rather than predicting future ones.

Before you rely on the result

Use the first day of proper bleeding, not spotting, and enter consecutive periods in oldest-to-newest order. The calculation does not confirm ovulation or diagnose PCOS, menopause or another condition. Seek advice for a persistent change, absent periods or troublesome symptoms.

Sources & further reading

Prepared by ProFertility · Updated 23 October 2026. Questions about your own circumstances? Contact our team.