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About the GST Calculator
GST is charged on the taxable value of a supply. Working forward from a base price is simple; working backwards from a price that already includes tax is where people get it wrong — you divide by (1 + rate), you do not subtract the rate.
Since the GST 2.0 reform of September 2025 the structure has been simplified to 0%, 5%, 18% and a 40% rate for luxury and sin goods. The 12% and 28% slabs no longer apply to most items.
The formula
Extracting GST from an inclusive price by simply subtracting the percentage overstates the tax — always divide.
Things worth knowing
Frequently asked questions
Four rates apply: 0% for exempt items, 5% for essentials, 18% as the standard rate, and 40% for luxury and sin goods such as tobacco and pan masala. The 12% and 28% slabs were withdrawn in the September 2025 reform.
Divide by (1 + rate ÷ 100). For an ₹11,800 price at 18%, the base is 11,800 ÷ 1.18 = ₹10,000 and the GST is ₹1,800. Subtracting 18% of ₹11,800 would give the wrong answer.
On a supply within a state the tax splits equally into CGST for the centre and SGST for the state. On a supply between states the full amount is levied as IGST, which the centre later apportions.
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