Ovulation Calculator

Estimate your ovulation date and most fertile days based on your last period and average cycle length.

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First Day of Your Last Period

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Average Cycle Length (days)

Typically between 21 and 35 days. Count from the first day of one period to the first day of the next.

Luteal Phase Length (days)

The time from ovulation to your next period. 14 days is average if you're unsure.

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Free Ovulation Calculator

Use this free ovulation calculator to estimate your ovulation date and fertile window based on the first day of your last period and your average cycle length. Knowing your fertile window can help you plan or avoid conception timing.

Ovulation typically occurs about 14 days before your next period starts, regardless of how long your overall cycle is. Your fertile window includes the five days before ovulation and the day of ovulation itself, since sperm can survive in the body for several days while the egg remains viable for roughly 24 hours after release.

How to Use the Ovulation Calculator

Enter the first day of your last period.
Enter your average cycle length and luteal phase length (use 14 days if unsure).
Click Calculate Ovulation Date.
View your estimated ovulation date, fertile window, and next expected period instantly.

Features

Estimates your ovulation date and full fertile window.
Adjustable cycle length and luteal phase for more personalized results.
Shows your next expected period date.
Mobile-friendly with print, share, copy, and download options.

Frequently Asked Questions

How is my ovulation date calculated?

Ovulation is estimated to occur 14 days before your next period starts (your luteal phase length), counted forward from the first day of your last period using your average cycle length.

What is the fertile window?

The fertile window is the span of days when pregnancy is most likely, generally the five days before ovulation through the day after ovulation.

Is this calculator accurate for irregular cycles?

This calculator gives a general estimate based on average cycle length. If your cycles are irregular, ovulation predictor kits or tracking basal body temperature may give more reliable results. Consult your doctor if you have concerns about your cycle.

Is this calculator free?

Yes, this ovulation calculator is completely free to use with no sign-up required.

Related Calculators

Already know you're expecting? Try our pregnancy due date calculator. Want to know how far along you are? Check the pregnancy week calculator. Curious about your baby's age after birth? Use the baby age calculator.

Last Updated: July 2026