Menstrual Cycle Length Calculator
Your average, shortest and longest cycle from past periods. Free, private and instant.
How to use the Cycle Length
- Add one row per entry for period start dates: First day of period.
- Press Calculate to get an instant result with a colour scale, chart and plain-English explanation.
About the Cycle Length
Add the first day of several past periods and this calculator works out the length of each cycle, your average, shortest and longest cycle and how regular you are. It then predicts your next period.
Also known as: cycle length calculator, average cycle length, how long is my cycle, menstrual cycle calculator.
Formula and cut-offs
Cycle length = days from the first day of one period to the first day of the next. Average = total cycle days / number of cycles. Regular cycles vary by 7 days or less.
Frequently asked questions
How do I calculate my cycle length?
Count from day 1 of one period to the day before day 1 of the next. Do this for several months and average them.
What is a normal cycle length?
21 to 35 days. Cycles in the first years after periods begin and near menopause vary more.
What counts as regular?
A cycle that varies by 7 days or less from month to month.
Sources and references
Written and checked by the MediHub editorial team against the sources above. Read how we build and review our calculators.
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Last updated . This calculator is for education only and is not medical advice. See the medical disclaimer.