Ovulation Calculator

Estimate your most fertile days and ovulation date from your last period and cycle length.

Read the guide: How to Find Your Fertile Window

How it works

  1. 1

    Enter your last period

    Add the first day of your most recent period.

  2. 2

    Set your cycle length

    Add your typical cycle length in days.

  3. 3

    See your window

    View your estimated ovulation day and fertile window.

Instant & 100% private — nothing is uploaded

Every calculation runs locally in your browser. The measurements, dates and details you enter stay on your own device and are never sent to a server — nothing is stored, logged or shared.

Frequently asked questions

When am I most fertile?
The fertile window spans roughly the five days before ovulation and the day of ovulation itself, when conception is most likely.
Can I rely on this for birth control?
No. Cycles vary and ovulation can shift, so calendar estimates are not a reliable method of contraception or a guarantee of conception.
Is this medical advice?
No. These calculators are for general information and education only. They are not a diagnosis or a substitute for professional care — talk to a doctor or qualified clinician about your health.