Ovulation & Fertility Calculator interactive tool
Calculator
Enter the first day of your last period and your average cycle length (days). Ovulation is estimated at about 14 days before your next period; the fertile window is the 5 days before ovulation plus the day of ovulation.
Result
Sat, Feb 15
Mon, Feb 10 - Sun, Feb 16
What Is Ovulation & Fertility?
If you are trying to conceive, timing is everything. An ovulation calculator helps you predict your fertile window—the specific days during your menstrual cycle when intercourse is most likely to result in pregnancy.
Understanding the Fertile Window
Your fertile window is determined by two biological facts: an egg only lives for about 24 hours after being released (ovulation), but sperm can survive inside the female reproductive tract for up to five days.
- Ovulation Day: Typically occurs about 14 days before your next expected period.
- High Fertility Days: The 5 days leading up to ovulation, plus the day of ovulation itself. Having intercourse during this 6-day window maximizes your chances of conception.
Who Should Use This Tool?
This calculator works best for women with regular menstrual cycles (typically between 21 and 35 days). If your cycles are highly irregular, mathematical estimates become less reliable, and you may want to use ovulation predictor kits (OPKs) or consult a fertility specialist.
How To Use the Ovulation & Fertility Calculator
- Enter the first day of your last period.
- Enter your average cycle length in days (e.g. 28).
- Review estimated ovulation date and fertile window (5 days before ovulation through day of ovulation).