Menstrual Cycle & Fertility Calendar
Predict your next periods, fertile window and most likely ovulation day from your own logged cycle starts, and see the phases laid out on a colour-coded calendar.
Used until you have logged at least two period starts.
12–14 days is typical; ovulation is placed this far before the next period.
Log actual period starts
Two or more logged starts replace the slider above with your own average cycle length, so predictions follow your body rather than the textbook.
No starts logged yet — predictions come from the last-period date and the sliders.
Everything you enter is stored only in this browser's localStorage, on this device. Nothing is sent to a server, and clearing your browser data deletes it.
Enter the first day of your last period, or log a period start, to build the calendar and predictions.
About this tool
Predictions are built backwards from the next expected period: ovulation is placed one luteal-phase length before it, and the fertile window is the five days before that plus one day after. Logging real period starts replaces the default cycle length with your own average. All data stays in this browser's localStorage — nothing is uploaded and no account is needed.
- 100% free — no account needed
- Runs in your browser
- Nothing is uploaded
Frequently asked questions
Is Cycle & Fertility Calendar really free?
Yes. Cycle & Fertility Calendar is completely free on PureBrowser — every feature, with no account, no trial, and no credit card.
Does Cycle & Fertility Calendar upload my data?
No. Cycle & Fertility Calendar runs entirely inside your browser, so anything you type, paste, or open stays on your own device.
Do I need to sign up or install anything?
Neither. There is no account and nothing to download — open the page and Cycle & Fertility Calendar is ready to use on desktop or mobile.
Does Cycle & Fertility Calendar work offline?
Once the page has loaded, yes. All of the processing happens locally in your browser, so it keeps working without a connection.
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