GST Calculator

Adding GST is a single step: multiply the base amount by the GST rate as a decimal, then add that GST to the base to get the total payable. Because GST is a flat percentage of the base, the tax scales directly with the amount.

In India, GST on an intra-state supply is collected in two equal halves: Central GST (CGST) and State GST (SGST). Each is exactly half of the total GST, so an 18% GST is levied as 9% CGST plus 9% SGST. The combined amount the buyer pays is identical to a single 18% charge — the split only governs how the revenue is shared between the central and state governments. For inter-state supplies a single Integrated GST (IGST) applies instead, at the full rate, with no split.

The reverse direction matters when a price already includes GST and you need the base value, for example to record the taxable amount on an invoice. Divide the GST-inclusive total by (1 + rate ÷ 100) rather than subtracting the percentage, because the GST was charged on the smaller base, not on the larger total. The formula is currency-agnostic; switch the currency at the top of the page to view your numbers in your own.

Take a 1,000 base amount at an 18% GST rate. The GST is 1,000 × 0.18 = 180, so the total with GST is 1,180. For an intra-state sale in India, that 180 splits equally into 90 CGST and 90 SGST. To reverse the calculation, divide the 1,180 GST-inclusive total by 1.18, which returns the original 1,000 base. Subtracting 18% of 1,180 instead would give 967.60, which is wrong, because GST was charged on the 1,000 base rather than on the 1,180 total.

India uses several GST slabs (commonly 0%, 5%, 12%, 18%, and 28%), so enter the slab that matches the specific item. The CGST/SGST split applies only to intra-state supplies; inter-state supplies use IGST at the full rate with no split. Some goods carry an additional cess on top of GST, which this calculator does not model — add it separately where it applies.