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🧾 Free GST Calculator

Add or remove GST in one step

Work out GST on any amount at any rate — forwards from a pre-tax price or backwards from a GST-inclusive total — and see the exact CGST, SGST and IGST split for your invoice. Free, no sign-up, and your figures never leave your browser.

Enter the pre-tax value of the goods or services.

GST rate

Standard rate for most goods and services

Slabs change. The current structure is 0%, 5%, 18% and 40% (plus 0.25%, 1.5% and 3% for stones, diamonds and bullion) after the 22 September 2025 rationalisation, which withdrew the 12% and 28% slabs — those two are kept here, tagged “withdrawn”, for reconciling older invoices.

Type of supply

Same state as your buyer? The tax splits in half as CGST + SGST. Different state? It is a single IGST line at the full rate. The amount of tax is identical either way.

Enter an amount and press Calculate GST to see the taxable value, the CGST/SGST split and the invoice total.

How the maths works

Adding GST to a price

GST = base amount × rate ÷ 100. On ₹1,20,000 at 18%, that is ₹21,600 of tax and a ₹1,41,600 invoice.

Removing GST from an inclusive price

This is the one people get wrong. You cannot just take 18% off the total. Base amount = total × 100 ÷ (100 + rate), and the GST is whatever is left over. ₹1,180 inclusive of 18% is ₹1,000 base plus ₹180 tax — not ₹967.60.

CGST, SGST and IGST

Selling inside your own state splits the tax into CGST and SGST at half the rate each — 18% becomes 9% + 9%. Selling to another state is a single IGST line at the full 18%. Your buyer pays the same either way; only the split on the invoice changes.

Which rate applies to me?

It depends on your HSN or SAC code, and the slabs are revised from time to time — the 12% and 28% slabs were withdrawn on 22 September 2025. Use the custom rate field for anything not in the chips, and check the current notification before you file.

Need billing software or a website?

Webknown builds GST-ready invoicing and websites for Indian businesses. Leave your details for a free, no-obligation chat. The calculator above stays free either way — we never see the amounts you type into it.