Privacy Policy
Last updated 19 August 2026
Period Calculator is a single static page. There is no account, no login, no server-side database and no API. Every date you type is used by JavaScript running inside your own browser tab, and the results are drawn on the page you are already looking at. Nothing you enter is transmitted to us, because there is nowhere for it to be transmitted to.
What we do not collect
- No name, email address, phone number or account of any kind.
- No period dates, cycle lengths, predictions or notes. These never leave your device.
- No cookies. The site sets none, for any purpose.
- No analytics, no page-view counting, no heatmaps, no session recording.
- No advertising or tracking scripts, and no social media pixels.
- No third-party fonts or CDNs. The two typefaces are bundled with the site itself, so loading this page does not tell any other company that you visited.
What is stored on your device
The tool uses your browser's own localStorage, which is readable only by this site on this device and this browser profile. We cannot see it. These are the only keys written:
| Key | What it holds | When it is written |
|---|---|---|
| periodcalc.v1 | Your last-period date, cycle length, period length and the shortest/longest cycle numbers. | Only while the "Remember my inputs on this device" box is ticked. Unticking it deletes this key immediately. |
| periodcalc.notes | Whatever you type in the notes box. | Saved as you type, independently of the remember box. Emptying the notes box clears it. |
| periodcalc.theme | Either "light" or "dark", so the page does not flash the wrong theme on load. | Saved when you use the theme toggle. |
Worth knowing: the notes box saves on its own key and does not wait for the "remember my inputs" tick box. If you want nothing kept at all, leave the notes box empty.
How to delete it
- Untick Remember my inputs on this device to erase the saved dates immediately.
- Clear the notes box to erase the saved notes.
- Or clear everything at once from your browser: use its "clear site data", "cookies and site data" or private-browsing controls for this site. Nothing survives that, because there is no copy anywhere else.
Calendar export, and the one case where data leaves your browser
The .ics download is generated in your browser and saved straight to your device, so it involves no server. The Google Calendar andOutlook buttons are different: they open those services with the predicted dates in the link, so once you click one, those dates are handled by Google or Microsoft under their own privacy policies. That is your choice to make, and nothing is sent until you click.
Hosting
The files are served by Cloudflare Pages. As with any website host, Cloudflare processes standard technical request information such as your IP address and browser user agent in order to deliver and protect the site. We have not added any analytics or reporting on top of that, and we do not build profiles of visitors.
Advertising
This site currently carries no adverts and loads no advertising scripts. If that ever changes, this page will be updated to name the provider and explain what it collects before the change goes live.
Children
We do not knowingly collect personal information from anyone of any age, because the site collects no personal information at all.
Changes to this policy
If the way the tool handles data changes, the date at the top of this page changes with it. The list of storage keys above is generated from the same file the calculator uses, so it stays accurate rather than drifting out of date.
Contact
See the contact page for how to reach us. Note that we cannot look up, change or delete "your data" on request, because we hold none of it. Deleting it is entirely in your hands, using the steps above.