Menstrual period calculator

The predictions are arithmetic, not a diagnosis: they step your own average cycle forward, and every date drifts when cycles vary. The fertile window assumes ovulation lands fourteen days before the next period, with sperm viable five days and the egg one day after; that is a textbook model, not a reading of your body. Cycles outside roughly 15 to 90 days, sudden changes, bleeding between periods, or severe pain are things to raise with a clinician; this tool cannot assess them. Everything you type stays in this tab unless you tick the remember box, which keeps a copy in this browser's local storage and nowhere else. The calendar file is built on your device and downloads directly.