How GST is worked out
To add GST, multiply the price by the rate: ₹1,000 at 18% has ₹180 of GST, so ₹1,180 in all. To take GST out of a price that already includes it, divide by 1 plus the rate: ₹1,180 ÷ 1.18 = ₹1,000, so the GST inside it is ₹180. The calculator does both to the paisa and shows the formula it used.
CGST and SGST, or IGST
When the seller and the buyer are in the same state, GST is split equally between the Centre (CGST) and the state (SGST, or UTGST in a union territory): 18% becomes 9% + 9%. When the goods or services go to another state, the whole amount is IGST. The total is the same; only who receives it changes.
The rates since 22 September 2025
Most goods and services are now taxed at 5% or 18%, with 40% for luxury and sin goods such as bigger cars, aerated drinks and, from 1 February 2026, cigarettes and pan masala. A few rates are special: 3% for gold and silver, 1.5% for cut diamonds, 0.25% for rough diamonds, and 0% for exempt goods like fresh milk and paneer. Not sure of the rate? Look up the item's HSN code.
Several items on one bill
Add a line for each item with its quantity, price and rate. The calculator totals them like a tax invoice: the taxable value and tax at each rate, the round-off to the nearest rupee, and the grand total in figures and in words.
Questions
How do I calculate 18% GST on an amount?
Multiply by 0.18 for the GST, or by 1.18 for the total. On ₹5,000 the GST is ₹900 and the total ₹5,900. Within a state that's ₹450 CGST and ₹450 SGST.
How do I remove GST from a total?
Divide the total by 1.18 for 18% (1.05 for 5%, 1.40 for 40%). The result is the price before GST and the difference is the GST: ₹1,050 including 5% GST is ₹1,000 plus ₹50.
Is GST included in the MRP?
Yes. An item with an MRP of ₹118 at 18% has ₹100 of value and ₹18 of GST; choose Remove GST to see the split.
Are 12% and 28% GST still used?
Not for goods: from 22 September 2025 the 12% and 28% slabs were folded into 5%, 18% and 40%. Look up the item's HSN or SAC code to be sure of its rate.
Should GST be rounded?
Each tax is worked out to the paisa. Invoices usually round the grand total to the nearest rupee and show the difference as round-off, as this calculator does.