Your Data Stays in Your Browser
Your broker CSV contains your entire trading history – every buy, sell, dividend, and corporate action. That's sensitive data. Before uploading it to any online tool, you should know exactly what happens to it. Here's how our calculator works.
Nothing is stored
When you use our CGT Calculator, your broker file is processed and the result is shown on screen. That's it. We don't save your file, your transactions, or your report to any database. When you close the tab, the data is gone.
There is no account, no login, and no "calculation history" feature – because we never store anything to show you later.
How the calculation actually works
The entire calculation engine runs inside your browser as WebAssembly (WASM). Your broker CSV is read by JavaScript running in your browser tab. The WASM engine applies HMRC's matching rules, converts foreign currencies, processes options strategies – all locally. The result is rendered on your screen without your trade data ever leaving your device.
Everything happens inside your browser. Your broker file is parsed, calculated, and turned into a report without ever being sent to a server. Our database has zero records of your trades — because we never receive them.
You can verify this yourself: open your browser's developer tools (F12), switch to the Network tab, and generate a report. You'll see requests for HMRC exchange rates and the WASM binary – but zero requests containing your trades or personal data.
No tracking, no ads
We use Vercel Web Analytics for basic page view counts. It doesn't collect personal data, doesn't use cookies, and doesn't fingerprint your browser. It's privacy-compliant by design.
We don't use Google Analytics, Facebook Pixel, or any advertising tracker. We don't sell data to anyone. There are no third-party scripts tracking your behaviour on the site.
Nothing to breach
Because we don't store your financial data, there is nothing for an attacker to steal. If our server were compromised, they would find zero transaction records – because we don't keep any.
This is a deliberate design choice. Many online tax tools store your data so they can offer features like "compare with last year" or "auto-fill from previous submission". We chose not to. Your data stays with you.
For more detail, see our Privacy & Security documentation.