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Free Ovulation Calculator

Estimate your ovulation date and fertile window from your last period and cycle length β€” with peak conception days, your next period, a pregnancy-test date, the due date if you conceive, and your next three cycles. Private and free.

Works offline once loaded
⚠️ This is an estimate based on a regular cycle and is not a method of contraception or medical advice. Cycles vary; for family planning or fertility concerns, talk to a healthcare provider.

πŸ”’ Your cycle dates never leave your device β€” everything is calculated in your browser.

Common uses

  • Ovulation Calculator by Last PeriodEnter the first day of your last period and your cycle length to estimate ovulation and your fertile window.
  • Fertile Window CalculatorFind the six fertile days each cycle β€” the five days before ovulation plus ovulation day itself.
  • When Will I Ovulate?See your next estimated ovulation date and how many days away it is, with the next three cycles projected.
  • Best Days to Get PregnantIdentify your peak-fertility days β€” the two days before ovulation plus ovulation day β€” to time conception.
  • Ovulation CalendarProject ovulation and fertile windows across the next several cycles and add them to your calendar.
  • Period CalculatorPredict when your next period is due from your last period and average cycle length.

How It Works

Estimates your ovulation date and 6-day fertile window from the first day of your last period and your average cycle length. Ovulation is placed by counting back the luteal phase (ovulation β†’ next period, usually ~14 days) from the next expected period, so longer or shorter cycles shift ovulation accordingly. Everything is computed in your browser.

  1. 1
    Enter the first day of your last period
    This is day 1 of your cycle β€” the first day of full menstrual flow, not spotting.
  2. 2
    Set your average cycle length
    The number of days from the first day of one period to the first day of the next (21–45 days). If you track it, open Advanced to fine-tune the luteal-phase length.
  3. 3
    See your fertile window
    You get the estimated ovulation date, the 6-day fertile window with the most-fertile peak days, your next period, the earliest pregnancy-test date, the due date if you conceive this cycle, and the next three cycles.
  4. 4
    Save the window
    Download an .ics calendar event for your fertile window, or copy the summary. Nothing is uploaded.

Cycle and fertility data is sensitive. Every calculation runs locally in your browser β€” your dates are never uploaded, logged, or stored.

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Frequently Asked Questions