Ovulation Calculator
Estimate your ovulation day and fertile window.
Result
Results are estimates for general information only and are not professional advice.
Ovulation timing
Ovulation usually happens about 14 days before the next period. This calculator estimates your ovulation day and the fertile window around it from your last period and cycle length. It is an estimate, not a contraceptive method.
Frequently Asked Questions
What is the Ovulation Calculator?
Estimate your ovulation day and fertile window. It runs instantly in your browser and is completely free to use.
What do I need to enter to use the Ovulation Calculator?
The Ovulation Calculator asks for the following values (2): First day of last period, Cycle length (days). Fill them in and the result appears immediately — the calculation runs on your own device, so nothing you type is sent to a server.
How accurate is the Ovulation Calculator?
The Ovulation Calculator uses standard, widely-accepted formulas, so its figures are reliable estimates for everyday planning. They are not a substitute for advice from a qualified professional.
Is the Ovulation Calculator free, and do I need an account?
Yes. The Ovulation Calculator — and every other calculator on Calculatis — is completely free, with no registration, no download and no limit on how often you use it.