GST Explained: Base Amount, Tax and Total Price

GST arithmetic starts with the amount and rate you select

The GST Calculator adds GST to a taxable value or separates GST from an amount that already includes tax. It uses the selected or custom rate as an arithmetic input; it does not determine the legally applicable rate for a supply.

Enter the amount and assumptions in the GST Calculator.

Adding GST to an exclusive amount

For ₹1,000.00 at 18% in the selected intra-state mode, the engine produces GST of ₹180.00. It splits that arithmetic amount into CGST of ₹90.00 and SGST of ₹90.00, giving an invoice total of ₹1,180.00.

Removing GST from an inclusive amount

For ₹1,180.00 inclusive of 18%, the engine recovers a taxable value of ₹1,000.00 and GST of ₹180.00. The selected intra-state split is CGST ₹90.00 and SGST ₹90.00.

Transaction type is a user-selected calculation assumption

In the selected intra-state mode the engine divides GST equally between CGST and SGST. In the selected inter-state mode it assigns the full amount to IGST. This selector does not determine place of supply or the legally applicable tax component.

For example, ₹1,120.00 inclusive at 12% in the selected inter-state mode gives a taxable value of ₹1,000.00, GST of ₹120.00 and IGST of ₹120.00.

Selected rates and calculator arithmetic are not compliance conclusions

The visible presets—0%, 3%, 5%, 12%, 18% and 28%—are arithmetic shortcuts, not a complete GST rate list. Custom rates remain available.

The calculator does not determine HSN/SAC classification, exemptions, nil- or zero-rated status, cess, reverse charge, composition treatment, place of supply, statutory valuation, return obligations or invoice compliance.

If your invoice differs, review Why a GST Calculator May Differ From an Invoice.