Menstrual Cycle Tracker

How to use the Menstrual Cycle Tracker

1. Enter the first day of your last period and your average cycle length.
2. Click Calculate to see your predicted next period, ovulation date, and fertile window.
3. Use Log today as period start to build a history stored in your browser.
4. Export your history as a CSV file at any time.

How ovulation is estimated

Ovulation typically occurs 14 days before the next period — or cycle length − 14 days after the start of the last period. For a 28-day cycle, this means day 14. Cycle length between 21 and 35 days is considered normal.

Privacy note

All data is stored exclusively in your browser's localStorage. Nothing is sent to any server.