Is there a quick way to find the GST inside a price without a calculator?

Yes. At 5%, divide the price by 21. At 18%, multiply the price by 9 and divide by 59. At 40%, divide the price by 3.5. Example: an MRP of ₹525 at 5% has ₹525 ÷ 21 = ₹25 of GST. A bill of ₹1,180 at 18% has ₹1,180 × 9 ÷ 59 = ₹180 of GST.

What if my bill has items at different GST rates?

Work out each item on its own with its own rate, then add the results. You cannot use one rate for the whole bill. Example: a bill has ₹1,050 of food at 5% and ₹590 of a service at 18%. The food has ₹50 of GST (₹1,050 ÷ 21). The service has ₹90 of GST (₹590 × 9 ÷ 59). The total GST on the bill is ₹140.

How do I split the GST into CGST and SGST?

If the seller and the buyer are in the same state, split the GST into two equal halves: CGST and SGST. If they are in different states, the whole amount is IGST. Example: ₹180 of GST on a sale within the state is ₹90 CGST + ₹90 SGST. The same ₹180 on a sale to another state is ₹180 IGST.

Does the same formula work for the 40% and 3% rates?

Yes. The formula is the same for every rate. Only the number changes. Example: a price of ₹14,000 at 40% gives ₹14,000 ÷ 1.40 = ₹10,000 before GST, so the GST is ₹4,000. A price of ₹1,03,000 at 3% (gold) gives ₹1,03,000 ÷ 1.03 = ₹1,00,000 before GST, so the GST is ₹3,000.

How to Remove GST From a Price (Reverse GST, With Examples)

Many prices in India already include GST. An MRP on a packet is one. A restaurant bill is another. So is an all-in quote from a service provider. Sometimes you need to know two things: what is the price before GST, and how much GST is inside it?

This is called a reverse GST calculation. It is a small sum, but many people get it wrong. This post shows the right way, a quick shortcut for each rate, and three worked examples.

The short version

Price before GST = price with GST ÷ (1 + rate ÷ 100).
GST = price with GST − price before GST.
Do not take the GST rate straight off the total. The tax was charged on the price before GST, not on the total.
Or use our Reverse GST Calculator, which does it for you and splits the tax into CGST, SGST and IGST.

Why 18% of the total is wrong

Say a shop gives you a bill of ₹1,180, and the GST rate is 18%.

Wrong: 18% of ₹1,180 = ₹212.40.
Right: ₹1,180 ÷ 1.18 = ₹1,000. The GST is ₹1,180 − ₹1,000 = ₹180.

The 18% was charged on ₹1,000, which was the price before GST. So the GST is ₹180. If you take 18% of ₹1,180, you make the tax ₹32.40 too high.

A shortcut for each rate

Each GST rate takes a fixed share of the price that already includes GST. If you remember the share, you can find the GST in one step.

GST rate	GST is this share of the price with GST	Easy way to find it
3% (gold, jewellery)	2.91%	price × 3 ÷ 103
5%	4.76%	price ÷ 21
18%	15.25%	price × 9 ÷ 59
40%	28.57%	price ÷ 3.5

The shares are rounded to two decimal places. The rates are those in force after the 22 September 2025 change. The 57th GST Council kept the 5%, 18% and 40% structure. Not sure which rate applies to your goods? Look up the item in our HSN/SAC Finder.

Three worked examples

1. A packet with an MRP of ₹525, GST at 5%. The price before GST is ₹525 ÷ 1.05 = ₹500. The GST is ₹25. The MRP already includes GST, so a shop cannot add GST on top of it. Sold within the state, the ₹25 is ₹12.50 CGST + ₹12.50 SGST.

2. A service provider says ₹2,360 for everything, GST at 18%. The price for the service is ₹2,360 ÷ 1.18 = ₹2,000. The GST is ₹360. If the provider is in another state, the whole ₹360 is IGST. If you are a registered business, you may be able to claim this ₹360 as input tax credit, but only if you get a proper tax invoice.

3. A bill of ₹14,000 at the 40% rate. The price before GST is ₹14,000 ÷ 1.40 = ₹10,000. The GST is ₹4,000.

When you need this

You agreed on an all-in price with a customer. On the GST invoice, you must show the price before GST (the taxable value), the CGST and SGST (or IGST), and the total separately. Work back to the taxable value first. Then enter it in our GST invoice generator.
You are checking a bill. Find the GST inside a restaurant or vendor bill to see if the tax is correct.
You want to add GST instead. Use the GST Calculator. It goes the other way: price before GST to price with GST.

Mistakes to avoid

Taking the rate off the total. This gives a tax amount that is too high.
Using one rate for a bill with different rates. Work out each item on its own.
Rounding too early. Keep the paise until the end, then round the final figures.
Forgetting the split. The invoice must show CGST and SGST, or IGST, not just one "GST" line.

Summary

Price before GST = price with GST ÷ (1 + rate ÷ 100).
GST = price with GST − price before GST.
At 18%, the GST is 15.25% of the price with GST. At 5% it is 4.76%.
An MRP already includes GST.
Within a state, split the GST equally into CGST and SGST. Between states, it is all IGST.

Sources

The formulas are plain arithmetic. The rates (3%, 5%, 18% and 40%) are as in force on 6 November 2026. Please check the rate for your goods before you issue an invoice. This is not legal advice.