GST Calculator

Goods and Services Tax (GST) is a unified indirect tax levied on the supply of goods and services. It replaced a patchwork of earlier taxes such as VAT, service tax, and excise duty with a single system. For transactions within a state, GST is split equally into CGST (collected by the central government) and SGST (collected by the state); for inter-state transactions, a single IGST at the full rate applies. An 18% GST on an intra-state sale, for instance, is charged as 9% CGST plus 9% SGST.

Goods and services are grouped into slabs. Essential items are taxed at 0% or 5%, standard goods and most services at 12% or 18%, and luxury or sin goods at 28%. Knowing which slab applies — and being able to quickly separate the tax from the price — is a daily necessity for business owners, freelancers, and anyone checking an invoice.

Adding GST (exclusive price): multiply the base amount by the GST rate. A service billed at 10,000 with 18% GST attracts 1,800 in tax, for a total invoice of 11,800.

Removing GST (inclusive price): this is where people often make mistakes. You cannot simply take 18% of the final price. The correct formula is:

Base Amount = Inclusive Price / (1 + GST Rate / 100)

For a bill of 11,800 that includes 18% GST, the base amount is 11,800 ÷ 1.18 = 10,000, and the GST component is 1,800. Taking 18% of 11,800 directly would give 2,124 — an overstatement of 324. This reverse calculation is essential when claiming input tax credit, filing returns, or checking whether a vendor has charged tax correctly.