Health
Menstrual Cycle Calculator
🔒 Runs in your browser
Calculate your next period date, ovulation window, and fertile days based on your last period and average cycle length. Free, instant, no data leaves your browser.
Typical: 21–45 days
Typical: 3–7 days
How to Track Your Menstrual Cycle (2026)
How to Track Your Menstrual Cycle — free online tool and guide with examples.