FastCalcs

Data and security

Last updated October 13, 2026

In short

  • Your numbers never leave your device. There is nothing for us to lose.
  • The whole site is encrypted with HTTPS. Browsers refuse to load it any other way.
  • No accounts, passwords, database or third-party scripts.
  • Found a security problem? Email hello@fastcalcs.app.

This page explains, in plain language, how FastCalcs is built to keep your information private and the site safe. Our privacy policy covers your legal rights.

Where your numbers go

Nowhere. When you open a calculator, your browser downloads the page and its small calculation code once. After that, every result is worked out on your own phone or computer. Nothing you type is sent to a server, so there is no record of your loan amount, your weight or your measurements anywhere but on your screen.

You can check this yourself. Load a calculator, switch off your internet connection, and keep typing: it still works.

Your numbers are also kept out of the page address. A link made with Copy link to this result carries them after a “#” sign, which browsers never send to any server, and the page removes them from the address as soon as it opens.

What we don’t have

  • No accounts or passwords, so there is nothing to steal or leak.
  • No database of users or results.
  • No cookies, analytics or ad trackers.
  • No third-party scripts. Every script and font is served from fastcalcs.app itself.

How the site is protected

  • HTTPS everywhere. The .app domain is on the browser preload list for HTTPS, so browsers will only ever connect to FastCalcs over an encrypted connection.
  • A static site. Pages are prebuilt files with no server-side code or database, which removes whole classes of attacks.
  • Strict security headers. A content security policy lets the browser run only our own code, and the site can’t be loaded inside another website’s frame.
  • Protected hosting. Our host, Cloudflare, protects the site against denial-of-service attacks and serves it from data centres around the world.
  • Tested code. Every formula is checked by thousands of automated tests before each update goes live.

If something changes

If we ever add advertising or analytics, they would bring some third-party code with them. We will update this page and our privacy policy before that happens, and explain what changes.

Reporting a security issue

If you find a vulnerability, please email hello@fastcalcs.app with the details and steps to reproduce it. Please give us a reasonable time to fix it before making it public, and don’t access other people’s data or disrupt the site while testing. Our contact details are also published at /.well-known/security.txt.