Ovulation Calculator
Estimate ovulation and fertile window from your cycle
Use this when you need a fast, accurate result — no sign-up, works entirely in your browser.
Estimated ovulation date—
Fertile window start—
Fertile window end—
Next period start—
How to Use
- Enter your details into the fields above.
- Click the calculate button to get your result instantly.
- Use the clear button to start a new calculation.
Example
- Last period 2026-09-01, 28-day cycle → Ovulation ≈ 2026-09-15, fertile window 2026-09-10 to 2026-09-16
- Last period 2026-03-01, 30-day cycle → Ovulation ≈ 2026-03-17; fertile window 03-12 to 03-18
Formula
Estimated ovulation = last period + (cycle length − 14) days. The fertile window is the 5 days before ovulation through the day after.
About Ovulation Calculator
Estimate ovulation and fertile window from your cycle. This free online tool gives you fast, accurate results without registration or downloads.
Everything runs locally in your browser, so your data is never uploaded or stored — privacy first.
Frequently Asked Questions
Is this tool free to use? +
Yes, it is completely free with no registration or download required.
Is my data private? +
Yes. Everything is processed locally in your browser. Nothing is uploaded or stored on our servers.
Does it work on mobile? +
Yes, it works on any device — phone, tablet, or desktop.