How to Add and Remove GST (With Simple Examples)

Goods and Services Tax (GST) is a consumption tax added to most goods and services. Whether you are a shopkeeper pricing an item, a freelancer raising an invoice, or a shopper checking a bill, it helps to know how to add GST to a price and how to remove it from a tax-inclusive total. The maths is simple once you see it.

Adding GST to a price

To add GST, you calculate the tax as a percentage of the base price and add it on:

GST amount = base price × (rate ÷ 100)
Total = base price + GST amount

Example: a product costs 1,000 before tax, at an 18% GST rate.

• GST = 1,000 × 0.18 = 180
• Total price = 1,000 + 180 = 1,180

Removing GST (the reverse calculation)

This is where people slip up. If a price already includes GST, you cannot just subtract the percentage - you have to divide:

Base price = total ÷ (1 + rate ÷ 100)

Example: a bill shows 1,180 including 18% GST.

• Base price = 1,180 ÷ 1.18 = 1,000
• GST included = 1,180 − 1,000 = 180

Notice that subtracting 18% of 1,180 (which is 212.40) would give the wrong answer. Always divide to back out tax.

CGST, SGST and IGST

For sales within a state, GST is split into two equal halves - CGST (central) and SGST (state). So 18% becomes 9% + 9%. For sales between states, it is charged as a single combined IGST at the full rate. The total tax is the same either way; only the split differs, which matters when you fill out an invoice.

The common GST slabs

In India, most items fall under one of four rates - 5%, 12%, 18%, or 28% - depending on the category of goods or services. Always apply the correct slab for the item you are pricing.

To skip the arithmetic, enter any amount into our free GST calculator and it will add or remove GST at any slab and show the CGST/SGST split instantly.