Ovulation Calculator

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.

First day of last period

Average cycle length (days)

Result

Estimated ovulation

Sat, Feb 15

Fertile window

Mon, Feb 10 - Sun, Feb 16

Next period (est.):Sat, Mar 1

What Is Ovulation?

If you are trying to conceive, an ovulation calculator can estimate an ovulation date and fertile window from a last-period date and average cycle length. Calendar estimates are less reliable when cycles vary.

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.
Fertile window: Often described as the five days before ovulation and the day of ovulation, but the timing can vary between cycles.

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 Calculator

Enter the first day of your last menstrual period in the designated field.
Input your average menstrual cycle length in days (typically 21-35 days).
Review the estimated ovulation date and fertile window.
Use these predictions for family planning or to better understand your cycle. Consult a healthcare provider if you have irregular cycles or specific fertility concerns.

Fertile window from cycle length

Use this ovulation calculator to estimate an ovulation date and fertile window from the last period and average cycle length. It assumes a regular cycle and should not be used as contraception or a diagnosis.