🧾GST calculator: add and remove GST

How is GST calculated?

To add GST, multiply the price by the rate and add the result. To take GST out of a price that already includes it, divide by one plus the rate. Subtracting the rate from the total gives the wrong answer, because the rate applies to the price before GST, not to the total.

Since the GST reform that took effect on 22 September 2025 there are two main rates, 5% and 18%, and a special 40% rate for a select few goods and services. Some items are exempt or at 0%, and a few, such as certain precious metals, have special rates, so use the rate shown for your item on the invoice or in the official rate schedule.

On an invoice GST appears as CGST and SGST for a sale within a state, or as IGST for a sale between states. The total tax is the same.

What is the formula for GST?

• Add GST: price with GST = price × (1 + rate ÷ 100), so GST = price × rate ÷ 100
• Remove GST: price without GST = price with GST ÷ (1 + rate ÷ 100), so GST = price with GST − price without GST
• Main rates: 5% merit rate, 18% standard rate, 40% special rate for a select few goods and services

Can you show a worked example of GST?

₹10,000 plus 18% GST: GST = 10,000 × 18 ÷ 100 = ₹1,800, so the total is ₹11,800. Going back, ₹11,800 ÷ 1.18 = ₹10,000, so ₹1,800 of the ₹11,800 is GST. At 5%, ₹1,000 becomes ₹1,050, and at 40%, ₹10,000 becomes ₹14,000.