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Home›Period & Fertility›Menstrual Cycle Calendar
Period & Fertility · Evidence-aware tool

Menstrual Cycle Calendar

Show observed and estimated cycle dates in a private local calendar with different visual treatment.

🔒 Inputs stay in this browser by default✓ Sources & limitations shown
Private tracker
Saved locally only
days
days
Your result
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Enter or adjust the values above, then calculate.

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    History exists only in this browser unless you export a backup. Clearing site data can remove it.

    Menstrual Cycle: observed & Estimated Cycle Dates

    Show observed and estimated cycle dates in a private local calendar with different visual treatment.

    Inputs this tool uses

    • Last period start
    • Typical cycle length
    • Typical period length

    What you get

    Estimated future cycle dates.

    Next estimated start2026-10-23

    How to use the Menstrual Cycle Calendar

    1. Enter last period start, typical cycle length, typical period length.
    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

    Observed period dates are stored locally; estimated future dates are derived and are not saved as observations. 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 2026-10-23. 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.

    Transparent arithmetic and unit conversionAG Health Tools methodology · 2026 · verified 2026-09-25Pure arithmetic tools, unit conversions and date mathTrying 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

    Connected tools

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

    ◌Period Calculator

    Estimate the next period date from recent cycle lengths or the last start date, showing uncertainty rather than a single guaranteed date.

    Open tool →    ◌Period Tracker

    Store observed period dates locally, derive cycle statistics and forecasts on-device, and keep estimates visually separate from observations.

    Open tool →    ◌Cycle Day Calculator

    Calculate cycle day from the last period start date and a target/current date using date-only arithmetic.

    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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