How to calculate GST (add or remove it, with examples)

To add GST to a price, multiply it by the rate and add the result: GST = price × rate ÷ 100, so ₹1,000 at 18% has ₹180 of GST and costs ₹1,180. To find the GST inside a price that already includes it, use GST = price × rate ÷ (100 + rate): ₹1,180 at 18% contains ₹180 of GST on a base price of ₹1,000. Within one state, that GST is split equally into CGST and SGST.

Add GST to a price

1. Multiply the price by the rate and divide by 100. ₹2,500 at 18%: 2,500 × 18 ÷ 100 = ₹450.
2. Add it to the price. 2,500 + 450 = ₹2,950.

A shortcut: multiply by 1.18 for 18% (or 1.05 for 5%). 2,500 × 1.18 = ₹2,950.

Remove GST from a price that includes it

This is where people often go wrong: taking 18% off ₹1,180 gives ₹967.60, which is not the price before GST. The right way:

1. Divide the price by (1 + rate ÷ 100). ₹1,180 ÷ 1.18 = ₹1,000, the price before GST.
2. Subtract to get the GST. 1,180 − 1,000 = ₹180.

Or in one step: GST = 1,180 × 18 ÷ 118 = ₹180.

CGST, SGST and IGST

• Within one state, GST is charged as CGST (central) and SGST (state), each half the rate. At 18%: 9% CGST + 9% SGST. On ₹2,500 that's ₹225 + ₹225.
• Between states, it's charged as IGST at the full rate: 18% on ₹2,500 is ₹450 of IGST.

The total is the same either way; only how it's split differs.

GST rates since 22 September 2025

After the GST rate changes that took effect on 22 September 2025, most goods and services in India use one of two main rates, 5% and 18%, with 40% for a small group of items and special rates such as 3% for gold. Many essential items are at 0%. The rate depends on what's being sold, so check the rate printed on your bill or the official rate lists; bills from before the change may still show 12% or 28%.

Do it in seconds (Sumfold)

1. Open the GST tab.
2. Choose Add GST or Remove GST, then type the amount.
3. Tap the rate (5%, 18%, 40% or 3%), or Other for any rate, including older rates or VAT in another country.

Sumfold shows the price before GST, the GST, the CGST and SGST halves and the total.

Common mistakes

• Taking the rate off a GST-inclusive price. Use the "remove" formula above.
• Adding CGST and SGST on top of each other at the full rate. They're halves of one rate, not two separate taxes of 18%.
• Rounding too early. Round only the final amounts, as bills do.