Menstrual & Fertility Tracking
Cycle Calculator
Predict your next period, ovulation day, and fertile window from your last period date. Runs entirely in your browser nothing leaves your device.
Next period
Oct 12, 2026
Ovulation day
Sep 28, 2026
Fertile window
Sep 23, 2026 → Sep 29, 2026
Current period ends
Sep 18, 2026
The Cycle math
Next period = last period + cycle length
Ovulation = next period − 14 days (luteal phase is the constant)
Fertile window = ovulation − 5 days to ovulation + 1 day
If you don't know your typical cycle length, log 3 cycles first. The average across cycles is more reliable than any single one.