GST Calculator
Enter an amount and a GST rate, then choose whether to add GST to a base amount or remove it from a GST-inclusive amount.
Overview
GST can be applied two different ways depending on what number you're starting from: adding it on top of a base price to get the final billed amount, or working backward from a GST-inclusive amount to find the original base price and the tax portion within it. This calculator handles both directions from the same form, so you don't need to remember which formula applies to which case.
Examples
Add 18% GST to 10,000
Amount: 10000, Rate: 18, Mode: Add GST
GST Amount: 1800.00 Total Amount (incl. GST): 11800.00
Remove 18% GST from 11,800
Amount: 11800, Rate: 18, Mode: Remove GST
Base Amount (excl. GST): 10000.00 GST Amount: 1800.00
How It Works
- Enter the amount and the applicable GST rate.
- Choose "Add GST" if your amount excludes tax, or "Remove GST" if it already includes tax.
- The GST amount and the resulting total or base value appear instantly.
FAQ
No. Every calculation runs locally in your browser.
Base amount = Total ÷ (1 + rate/100). The GST amount is then the difference between the total and the base amount — dividing by the rate directly would overstate the tax.
Yes. Enter any rate — common slabs are 5%, 12%, 18%, and 28%, but the calculator works with any percentage you enter.
No. This calculator works with a single combined GST rate — split it into CGST/SGST halves yourself if your invoice needs that breakdown.