VAT Calculator

WHAT IT DOES

VAT Calculator handles all your Value Added Tax calculations with two complementary modes. "Add VAT to net price" computes the VAT amount and gross total when you know the price excluding VAT. "Extract VAT from gross price" works backwards — when you have a total that already includes VAT, it calculates the net amount and the VAT portion. Both modes display the net amount, VAT amount, gross amount, and the applied VAT rate in real-time. The panel supports multiple VAT rates with customizable presets so you can quickly switch between rates commonly used in different countries or for different product categories.

WHERE IT RUNS

This script runs on every website you visit. Whether you are preparing invoices, reviewing purchase orders, comparing prices across European retailers, working with expense reports, or managing accounting data in a web application, the panel is always available. It works alongside your existing tools without interfering with your workflow.

HOW TO USE

Select your calculation mode from the dropdown menu. Choose a preset VAT rate by clicking one of the percentage buttons, or type a custom rate in the custom field. Enter the amount in the input field — results update automatically. Click the "Copy Result" button to copy the gross amount with net amount to your clipboard. Custom rates can be saved as presets by typing your desired rate and clicking "Set Custom" — the panel remembers your custom presets across sessions. Click any history entry to reload previous calculations.

THE ACCURATE ROUNDING MECHANISM

VAT calculations must handle financial rounding correctly to match real-world business requirements. The calculator uses precise mathematical operations that apply the VAT rate to the exact net amount first, then rounds the resulting VAT and gross amounts independently to two decimal places. This two-step rounding approach prevents the common error of applying VAT to an already-rounded number, which can result in discrepancies of a few cents. The extraction mode uses the inverse formula (gross ÷ (1 + rate)) to determine the net amount, maintaining consistency with standard accounting practices.

THE PANEL

The panel is fully draggable and remembers its position per site. It minimizes to a compact floating bubble when collapsed. All settings — custom VAT presets, default rate, and calculation history — persist across browser sessions using GM_setValue storage. Press the Escape key to close the panel. The panel automatically focuses the amount input field for quick keyboard entry.

PLEASE NOTE

This script requires the free BotGentz extension to run. VAT rates vary by country and product category — always verify the correct rate for your specific situation. Websites change their structure and behavior over time; if any functionality stops working, the script may need an update. No user data is sent anywhere — all calculation history, presets, and settings are stored locally in your browser. The script never reads or modifies password, hidden, or file input fields.