Ovulation Calculator
Find your most fertile days and ovulation window from your cycle.
About the Ovulation Calculator
The AlarmDaddy Ovulation Calculator estimates your fertile window and likely ovulation day based on your last period and average cycle length. For couples trying to conceive, the days leading up to and including ovulation are the most fertile — typically a six-day window ending on ovulation day.
Enter the first day of your last period and your average cycle length. The calculator estimates your ovulation date, your fertile window, and your next expected period. It is a planning aid based on cycle averages, not a contraceptive method — cycles vary, and ovulation can shift month to month.
How to use this calculator
- 1Enter the first day of your last period.
- 2Enter your average cycle length.
- 3Read your estimated ovulation date, fertile window, and next period date.
The formula
Ovulation typically occurs about 14 days before the next period, regardless of cycle length. Sperm can survive up to five days, so the fertile window spans the five days before ovulation plus ovulation day itself.