How to use the GST calculator
This GST calculator helps you add GST to a base amount or remove GST from a GST-inclusive price. Enter the amount, choose a GST rate and select the calculation mode to see the base amount, tax amount and final amount.
Adding GST
When adding GST, the calculator applies the selected rate to the base amount. For example, 18% GST on ₹1,000 is ₹180, giving a final price of ₹1,180.
Removing GST from an inclusive price
When the entered amount already includes GST, the calculator separates the taxable base from the GST portion. This is useful when checking invoices, receipts and quoted prices.
GST rates and tax rules can change. Verify the applicable rate for your goods or services with an official or qualified source before filing or making a tax decision.
GST formulas and a worked example
When adding GST to a pre-tax price, calculate GST = base amount × rate ÷ 100, then add that tax to the base amount. For example, 18% of ₹1,000 is ₹180, so the GST-inclusive price is ₹1,180.
When the entered price already includes GST, calculate base amount = inclusive price ÷ (1 + rate ÷ 100); the GST portion is the inclusive price minus that base amount. At 18%, ₹1,180 ÷ 1.18 = ₹1,000 before tax and ₹180 GST (subject to rounding).
What the GST result does and does not tell you
The calculator applies the rate you select; it does not determine the legally applicable rate for a product or service. The available rates are common presets, not a complete classification of every supply. GST rate changes for many goods and services took effect on 22 September 2025, and some supplies have different or special rates. Check the current rate, classification, effective date and any exemptions against official guidance before using the result for an invoice or return. Depending on the transaction, GST may be split into CGST and SGST or charged as IGST; this calculator reports the combined GST amount rather than classifying the transaction.
For official information, visit the Central Board of Indirect Taxes and Customs (CBIC) website. Keep the supplier invoice and transaction details as the authoritative record.