How to use GST Calculator
When the price is before GST, multiply the base by the rate to find the tax and add it to the base. When the price already includes GST, divide by one plus the rate to recover the original taxable amount. Subtracting the rate directly from an inclusive price is not the same calculation.
The rate is your input. The example 18% does not establish the correct rate for a product or service. Classifications, exemptions, place of supply, invoice requirements and current rules must be checked separately with an appropriate source.
The formula
A worked example
Amount (₹): 1000 · GST rate (%): 18 · Calculation: Add GST to a base amount
GST-inclusive amount: ₹1,180.00
The rate is entered by you. This tool does not identify product classifications, applicable rates, exemptions or filing treatment.
Questions about this calculation
Does this determine the right GST rate?
No. Enter the applicable rate after checking the current classification and rules.
Why can’t I subtract 18% from an inclusive total?
The 18% tax is measured on the base, not the inclusive total. Divide by 1.18 to recover the base for that illustrative rate.
Formula checks: 2026-10-08. Assumptions & corrections.