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
Aug 27, 2026
Ovulation day
Aug 13, 2026
Fertile window
Aug 8, 2026 → Aug 14, 2026
Current period ends
Aug 3, 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.