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    Ovulation calculator: find your fertile window

    Estimate your ovulation day and the six-day fertile window around it from your last period and cycle length. Calculated in your browser — no account, no data leaves your device.

    Estimated ovulation day

    Sat, 5 September 2026

    Your fertile window

    • Mon, 31 August 2026
    • Tue, 1 September 2026
    • Wed, 2 September 2026
    • Thu, 3 September 2026
    • Fri, 4 September 2026
    • Sat, 5 September 2026 · ovulation
    • Sun, 6 September 2026

    Next period expected Sat, 19 September 2026.

    Emmenia

    My estimated fertile window

    31 Aug – 6 Sept

    Ovulation (est.)
    5 Sept
    Cycle length
    28 days
    Next period
    19 Sept

    Estimate for wellness planning — not contraception or medical advice.

    The card only contains the dates you entered here — no account details, and nothing is uploaded.

    Why we count backwards from your next period

    The second half of the cycle — from ovulation to the first day of bleeding — is fairly fixed at around 14 days for most people. The first half is what stretches and shrinks. So the most reliable way to estimate ovulation from dates alone is to find your predicted next period and count back a fortnight, which is exactly what this calculator does.

    Signs worth tracking alongside the dates

    • Cervical mucus: becomes clear, slippery and stretchy in the days before ovulation.
    • Basal body temperature: rises slightly and stays up after ovulation has happened.
    • Mittelschmerz: a brief one-sided ache some people notice mid-cycle.
    • Energy and libido: often peak around the fertile window.

    Logging those signals next to your dates over a few cycles is what turns a generic estimate into a pattern you can actually rely on.

    Common questions

    When do you ovulate in a cycle?
    Ovulation usually happens about 14 days before your next period starts, not 14 days after the last one began. On a 28-day cycle those land on the same day, but on a 34-day cycle ovulation is nearer day 20 than day 14.
    How long is the fertile window?
    Roughly six days: the five days before ovulation plus the day itself. Sperm can survive several days in the reproductive tract, which is why the days leading up to ovulation matter as much as the day itself.
    What are the signs of ovulation?
    Common ones are clear, stretchy cervical mucus, a small rise in resting body temperature after ovulation, mild one-sided pelvic twinges, and a change in libido. Tracking two or three of these together is far more reliable than a calendar estimate alone.
    Can this calculator confirm I ovulated?
    No — it estimates timing from dates alone. Ovulation predictor kits, basal body temperature charts and clinical testing are what confirm it. If you are trying to conceive and cycles are irregular, speak to a clinician.

    Want this worked out for you, every cycle?

    Emmenia learns your real cycle from what you log, predicts cramps before they start and builds a daily relief plan. Free to start.

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    These calculators give estimates for general wellness planning. They are not contraception, not a pregnancy test and not medical advice. Speak to a clinician about pain, bleeding or cycle changes that worry you.