Ovulation Calculator
Your fertile window, ovulation day and next periods.
Estimates only — not a method of contraception. Irregular cycles make predictions less accurate.
For information only — not a diagnosis or medical advice. Nothing you enter is sent or stored.
How to use Ovulation Calculator
- Enter the first day of your last period.
- Enter your average cycle length.
- Click “Calculate” to see the next three cycles.
Frequently asked questions
How reliable is this?
It's based on averages. Cycles vary, especially if they're irregular. Ovulation tests or tracking temperature give a closer picture.
Can I use this as birth control?
No. Calendar estimates are not reliable enough to prevent pregnancy.
Can this replace a doctor?
No. This tool gives general estimates and self-checks for information only. It does not diagnose anything. Please see a qualified health professional for medical advice, and seek urgent care if you feel unwell.
Is Ovulation Calculator free?
Yes. Ovulation Calculator is free to use with no sign-up and no watermark.
Is my information saved or sent anywhere?
No. Everything is calculated in your browser. Nothing you enter is sent to a server or stored.
Does it work on my phone?
Yes. It works in any modern browser on Windows, Mac, Linux, Android and iPhone. Very large files may be slow on older phones.