How to Calculate GST in India
6 min read · Updated September 26, 2026 · by Thomas M, Registered Investment Adviser (South Carolina)
GST arithmetic is simple once you know whether the price already includes the tax. This guide shows how to add and remove GST, how the tax is split between the Centre and the State, and the current slabs.
Current GST slabs
Since 22 September 2025 the main rates are 5% and 18%, with 40% for sin and luxury goods, plus special rates such as 3% on gold and 0.25% on rough diamonds, and nil for many essentials. The older 12% and 28% slabs no longer apply to new supplies. Check the rate for your item’s HSN or SAC code on the GST portal.
Adding GST
GST = price × rate. On ₹10,000 at 18%, GST is ₹1,800.00 and the total ₹11,800.00.
Removing GST
Price before GST = total ÷ (1 + rate), not total × (1 − rate). ₹11,800 including 18% GST is ₹10,000.00 before tax.
CGST, SGST and IGST
Within a state, GST splits equally: ₹1,800 becomes CGST ₹900.00 and SGST ₹900.00. Between states, the whole amount is IGST (₹1,800.00).
Tools
Use the GST calculator India for a quick answer and the invoice generator to prepare a bill. Confirm treatment with the GST portal or a professional.
Practice questions
Test yourself, then tap to check. Answers are calculated by the tools linked below.
- A bill totals ₹23,600 including 18% GST on a local sale. What is the CGST?
Show answer
Price before GST: ₹20,000.00 · Total GST: ₹3,600.00
- A$330 includes 10% GST. How much is the GST?
Show answer
Price before tax (net): A$300.00 · GST included: A$30.00
Frequently asked questions
How do I calculate GST?
Multiply the price by the GST rate and add it to the price. To remove it, divide the total by 1 plus the rate.
What is the 18% GST formula?
Total = price × 1.18; GST = price × 0.18; GST inside a total = total × 18 ÷ 118.
What is the difference between CGST, SGST and IGST?
CGST and SGST are the Centre’s and State’s halves of GST on local sales; IGST is the whole tax on inter-state sales.
Did GST rates change in 2025?
Yes, from 22 September 2025 the structure moved to 5%, 18% and 40% with special rates.
Try it yourself
GST Calculator IndiaAdd or remove GST at 5%, 18% or 40%, with the CGST + SGST or IGST split.GST CalculatorAdd or remove GST on a price, with New Zealand 15%, Australia 10% and Canada’s 5% federal rate presets.
Invoice GeneratorCreate a clean invoice with line items, tax, discount and totals, then print it or save it as a PDF — free, no sign-up.Keep learning
How to Calculate Sales Tax, VAT and GST6 min readHow to Write an Invoice6 min readHow to Calculate Percentages7 min readReviewed by Thomas M, Registered Investment Adviser (South Carolina), who launched his own financial advisory firm in 2010. Spot a mistake? Tell us. See our editorial policy. Finance content is educational and not financial advice; see the disclaimer.