Menstrual Cycle Predictor (Local-Only)

How to use

1. Fill the fields above — results update as you type.
2. Adjust any input to compare scenarios instantly.
3. Nothing is uploaded; everything runs in your browser.

General information only — not medical, financial or legal advice. Figures cross-checked against public official sources (IRS / HMRC / NHS / WHO guidance) as of 2026-08. For decisions that matter, confirm with a licensed professional in your country.

About this tool

Calendar method: ovulation ≈ cycle length − luteal phase; fertile window spans the 5 days before plus day after. Runs 100% locally — period data is exactly the kind of thing that should never touch a server.

FAQ

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Your rating stays in this browser (local storage) — nothing is sent to any server.