Fertility Calculator

Free fertility calculator to estimate ovulation window. Instant results in your browser — no signup.

JavaScript is required for live calculation.

You can still read how Fertility Calculator works, the formula, examples, and FAQs below.

Date
Days to add (+) or subtract (−)

Direct calculator

Enter values and calculate an instant answer.

Inputs

Enter the values, then calculate.

Date

Days to add (+) or subtract (−)

Results update when you click Calculate.

Result

Primary answer and useful breakdowns.

Estimated ovulation

Feb 14, 2026

Days changed

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Recently used

Tools you open will show up here on this device — with your last inputs when available.

What this result means

Free fertility calculator to estimate ovulation window. Instant results in your browser — no signup. Estimate ovulation window using cycle length; last period. Result: estimated ovulation/fertile window.

Assumptions

Rule dependency: Clinical guideline / formula; may vary by jurisdiction.

How it works

Estimate ovulation window using cycle length; last period. Result: estimated ovulation/fertile window.

Example

Example: “ovulation calculator”. Enter your values and click the button to get a result.

Frequently asked questions

What does this ovulation window calculator do?+

It helps you estimate ovulation window. Typical search: “ovulation calculator”.

How should I read the result?+

Estimate ovulation window using cycle length; last period. Result: estimated ovulation/fertile window.