Period Cycle Tracker
Enter your last period start date and your average cycle length. This tool predicts your next period, your estimated ovulation day and your fertile window, and keeps a private log of your actual start dates right in your browser.
Next period: —
—
—
Estimated ovulation day: —
Fertile window: —
Fertile window: —
Next 3 cycles
Log a period
Record the real start date of a period. Logging real dates makes future predictions more accurate. Everything is saved only in this browser.
Period history
Please note: Cycles vary from month to month, so all dates on this page are estimates only and this tool is not medical advice. If your periods are very irregular or you have health concerns, please see a doctor.
How to use
- Enter the first day of your most recent period and your average cycle length.
- Press Calculate — you will see your next predicted period, ovulation day and fertile window.
- When a period actually starts, log it in the history section so your record stays accurate.
Tips
- The most common cycle length is 28 days, but anything between 21 and 45 days is entered regularly.
- Logging at least 3 real start dates gives you a much better picture of your own pattern.
- Ovulation is estimated as 14 days before the next predicted period; the fertile window covers 5 days before to 1 day after that estimate.
- This data never leaves your browser — no account and no tracking.