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GST-exclusive and GST-inclusive calculations, CGST/SGST vs IGST, and the formulas behind both — with worked examples at current GST 2.0 rates.
Checked against current rules for GST 2.0 rate slabs on 29 September 2026. Source: CBIC Notification No. 9/2025-Central Tax (Rate).
Every GST calculation, however complicated the transaction looks, comes down to one of two directions: either you know the price before tax and need to add GST on top, or you know the final price a customer actually paid and need to work backward to find how much of it was GST. Get comfortable with both directions and the rest — CGST/SGST splits, IGST, invoices — falls into place quickly.
GST (Goods and Services Tax) is India's unified indirect tax on the supply of goods and services, charged as a percentage of the transaction value. It replaced a layered system of central and state taxes with a single tax that's still split between the Centre and the state (or charged in full to the Centre for inter-state supply — more on that below). The rate that applies depends on how the goods or services are classified, not on who's buying or selling.
This is the direction you use when you know your price before tax — a quotation, a cost price, a service fee — and need to work out what the customer will actually pay once GST is added.
Worked example
Base amount ₹1,000, GST rate 18%. GST = 1,000 × 18 ÷ 100 = ₹180. Final amount = 1,000 + 180 = ₹1,180.
This is the reverse direction — you know the final, GST-inclusive amount (what actually appears on a receipt or bank statement) and need to find the pre-tax base amount and the GST portion hidden inside it. You cannot simply subtract the GST percentage from the total; GST is calculated as a percentage of the base, not of the final amount, so the formula has to divide, not subtract.
Worked example
Inclusive amount ₹1,180, GST rate 18%. Base amount = 1,180 ÷ 1.18 = ₹1,000. GST amount = 1,180 − 1,000 = ₹180.
This reverse calculation is covered in more depth, with more worked examples, in our dedicated guide on calculating GST from a total amount.
Free GST Calculator
Calculate GST, CGST, SGST and IGST from a base amount, or reverse-calculate the base amount and GST from a GST-inclusive total — no signup required.
What is the formula to calculate GST?
GST Amount = Base Amount × GST Rate ÷ 100. Add that to the base amount to get the final, GST-inclusive amount. For example, ₹1,000 at 18% GST adds ₹180 GST for a ₹1,180 final amount.
What are the current GST rates in India?
Under GST 2.0 (effective 22 September 2025, per CBIC Notification No. 9/2025-Central Tax (Rate)), the main slabs are 0%, 5% and 18%, with a 40% rate on select demerit/luxury goods and a special 3% rate on gold, silver and precious stones. The earlier 12% and 28% slabs were removed — most 12% items moved to 5% or 18%, and most 28% items moved to 18%.
Does this calculator tell me which GST rate applies to my product?
No. A GST calculator computes GST based on the rate you supply — it does not determine the legally applicable rate for a specific product or service, which depends on its HSN (goods) or SAC (services) classification under CBIC's rate schedules.
GST & Tax
GST Inclusive vs GST Exclusive: What's the Difference?
What GST-inclusive and GST-exclusive prices mean, how to convert between them, and when each calculation is the right one to use — with worked examples.
GST & Tax
CGST, SGST and IGST Explained
What CGST, SGST and IGST are, how GST splits between them based on intra-state vs inter-state supply, and how to calculate each — with practical examples.
Once you know the total GST amount, it's charged as one of two combinations, depending on where the buyer and seller are located:
| Supply type | Who's charged | How GST splits |
|---|---|---|
| Intra-state (same state) | CGST + SGST | GST amount split equally — half CGST, half SGST |
| Inter-state (different states) | IGST | Full GST amount charged as IGST, not split |
So on the same ₹1,000 base at 18% GST: an intra-state sale charges ₹90 CGST + ₹90 SGST (₹180 total), while an inter-state sale charges ₹180 IGST. The total tax collected is identical either way — only how it's labelled and distributed between the Centre and the state changes. This is covered in full, with the reasoning behind it, in our CGST, SGST and IGST explainer.
As of GST 2.0, effective 22 September 2025 under CBIC Notification No. 9/2025-Central Tax (Rate), the standard slabs are 0%, 5% and 18%, with a 40% rate reserved for a short list of demerit and luxury goods, and a special 3% rate for gold, silver and precious stones. The previous 12% and 28% slabs no longer apply to new transactions — most 12% items were moved to 5% or 18%, and most 28% items were moved to 18%.
The rate you enter isn't decided by the calculator
A GST calculator computes GST based on the rate you supply. It does not determine the legally applicable GST rate for a particular product or service — that depends on the item's HSN or SAC classification, which you should confirm against the current CBIC rate schedule or a tax professional if you're unsure.
For quick, repeatable calculations in either direction — with the CGST/SGST/IGST split done automatically — use the free GST calculator below. Once you have your numbers, you can turn them straight into a GST-compliant invoice with the GST Invoice Generator.
Free Selling Price & GST Margin Calculator
Work out your selling price from cost and a target margin or markup, and see the GST-inclusive or GST-exclusive customer price, profit and effective margin instantly — no signup required.