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Health Tools

Menstrual cycle calculator

See your current cycle and the next few, with the estimated period start, ovulation day and fertile window for each.

Select the date your most recent period started.

Usually between 20 and 45 days. The average is 28.

Frequently asked questions

How does the menstrual cycle calculator work?

It maps your current and upcoming cycles from the first day of your last period and your average cycle length, showing the estimated period start, ovulation day, and fertile window for each cycle.

What is a normal menstrual cycle length?

Most cycles last between 21 and 35 days, with 28 days a common average. Cycles that fall well outside this range, or that vary a lot, are worth discussing with a healthcare professional.

Why does my cycle change from month to month?

Stress, sleep, travel, illness, exercise, and natural hormonal changes can all shift your cycle. Some variation is normal; tracking over several months gives a clearer picture.

Is the information I enter private?

Yes. The calculation runs entirely in your browser. Evecare never sees, stores, or transmits anything you enter.