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Ovulation Calculator

Estimate your ovulation day and fertile window from your last period.

Count from the first day of one period to the first day of the next.

This is a calendar estimate only. Ovulation timing varies between cycles, and it cannot detect whether you actually ovulated. It is not contraception, and it should not be used to prevent pregnancy.

Estimated ovulation

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Fertile window

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Next period

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Days until ovulation

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Next three cycles

CyclePeriod startsFertile windowOvulation

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What Is Ovulation Calculator?

The Ovulation Calculator estimates your ovulation day and fertile window from the first day of your last period and your average cycle length, then projects the next three cycles.

Who Uses the Ovulation Calculator?

People use it to understand roughly when in the cycle ovulation tends to fall and to plan accordingly. It is a calendar estimate and cannot confirm that ovulation occurred.

How to Use the Ovulation Calculator

  1. Enter the first day of your last period.
  2. Enter your average cycle length.
  3. Read the estimated ovulation day and fertile window.

Why Choose Our Ovulation Calculator?

  • Longer cycles push the estimate later in the cycle
  • Fertile window spans five days before ovulation
  • Projects the next three cycles

Try the Ovulation Calculator above — it is free, fast, and works on any device. Bookmark this page to return whenever you need it.