Ovulation and fertile window calculator
Calculate your fertile days and ovulation.
How to useYour fertile window.
Estimate for regular cycles. Don’t use it as birth control.
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Ovulation and fertile window calculator: what it is for
The calculator shows your fertile days and likely ovulation day from the first day of your last period and your cycle length.
It's an estimate and shouldn't be used as a method of birth control.
How to use
- Enter the first day of your last period.
- Enter your cycle length.
- See your fertile window and ovulation.
When to use it
- Planning a pregnancy.
- Getting to know your cycle.
- Tracking ovulation.
Frequently asked questions
Is it really free?
Yes, 100% free. No sign-up, no subscription and no usage limits. All Tools123 tools are free and run right in your browser.