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Home›Period & Fertility›Fertile Window Calculator
Period & Fertility · Evidence-aware tool

Fertile Window Calculator

Estimate a broad fertile window around ovulation and explicitly state that the result is not contraception.

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Enter or adjust the values above, then calculate.

    Fertile Window: estimate Fertile Days

    Estimate a broad fertile window around ovulation and explicitly state that the result is not contraception.

    Inputs this tool uses

    • Estimated/observed ovulation date

    What you get

    Broad estimated fertile window around the entered ovulation date.

    Estimated window2026-09-20 – 2026-09-26

    How to use the Fertile Window Calculator

    1. Enter estimated/observed ovulation date.
    2. Select any method, activity level or option shown on this page, then choose Calculate.
    3. Read the main result together with the supporting values, method, assumptions and limitations below before using the estimate.

    How this calculation works

    Cycle tools use date arithmetic from observed period starts and user-entered cycle assumptions. Estimates are never presented as contraception.

    Method transparency: Results are calculated from the values you enter. Health estimates are educational reference values, not diagnoses or treatment advice.

    Example calculation

    The sample values loaded into the calculator produce 2026-09-20 to 2026-09-26. This example exists to show how the output is structured; replace the sample values with your own inputs for your calculation.

    Assumptions and limitations

    • Cycle and ovulation dates are estimates and can vary from cycle to cycle.
    • This tool is not contraception and does not diagnose fertility or pregnancy.

    Sources and review status

    Source set last verified 2026-09-25. No clinician review is claimed unless a real named reviewer is displayed.

    Trying to Get Pregnant? Here’s When to Have SexAmerican College of Obstetricians and Gynecologists · current · verified 2026-09-25Ovulation timing and broad fertile-window contextYour menstrual cycleU.S. Office on Women’s Health · current · verified 2026-09-25Menstrual-cycle and ovulation timing contextPregnancy testsU.S. Office on Women’s Health · current · verified 2026-09-25Home pregnancy-test timing and uncertainty

    Questions people ask about Fertile Window Calculator

    Is the fertile window exact?

    No. It is a broad estimate around an entered or estimated ovulation date. Ovulation can vary from cycle to cycle and the result is not contraception guidance.

    Connected tools

    Continue with the closest related calculation without re-entering sensitive values automatically.

    ◌Ovulation Calculator

    Estimate ovulation from the expected next period minus an editable luteal-phase assumption and show the assumption used.

    Open tool →    ◌Luteal Phase Calculator

    Calculate luteal-phase length from an observed/estimated ovulation date and next period start.

    Open tool →    ◌Pregnancy Test Date Calculator

    Estimate an earliest/recommended pregnancy-test window from expected period or ovulation timing and defer to test instructions.

    Open tool →
    Medical boundary: AG Health Tools provides educational wellness estimates and private tracking utilities. It does not diagnose conditions, recommend treatment, calculate medication doses, or replace a clinician.
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