Ovulation & Fertile Window Calculator
Estimate an ovulation date and fertile window from the first day of your last period.
Your estimated dates will appear here.
Estimated six-day fertile window
- Estimated ovulation
- Expected next period
This uses the ASRM six-day definition: the five days before estimated ovulation plus the estimated ovulation day. Actual fertile timing can fall outside a calendar estimate.
Calendar estimates cannot predict ovulation exactly and should not be used as birth control. Irregular cycles make estimates less reliable.