Ovulation Calculator

Estimate your ovulation day & fertile window

Estimated ovulation
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Ovulation Calculator — guide & how to use

What it does

The Ovulation Calculator estimates your most fertile days from the first day of your last period and your cycle length. It shows your estimated ovulation day, your fertile window, your next period, and a pregnancy due-date estimate if you conceive this cycle — calculated privately in your browser, free.

How to use it

  1. Enter the first day of your last period.
  2. Enter your average cycle length (commonly 28 days).
  3. Read your estimated ovulation and fertile window, plus your next period and due-date estimate.

How to embed this tool on your website

No account, no coding. Copy the embed code and paste it where you want it to appear:

<iframe src="https://snaptoolsuite.com/ovulation-calculator/?embed=1"
  style="width:100%;max-width:560px;height:760px;border:0;"
  title="Ovulation Calculator" loading="lazy"></iframe>
<p>Free <a href="https://snaptoolsuite.com/ovulation-calculator/">Ovulation Calculator</a> by Snap Tool Suite</p>
2 Paste it on your page
3 It just works

See it live: view a real embed example →

Frequently asked questions

How do you calculate ovulation?

Roughly the first day of your last period plus (cycle length − 14). The fertile window is ~5 days before ovulation through the day after.

How accurate is it?

It's an average-based estimate and varies by person and month. Combine with ovulation tests or a doctor for decisions.

Is it really free?

Yes. 100% free, everything runs in your browser.

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🔒 Everything is calculated in your browser. We don't store or sell your data. Estimate only — not medical advice.