How do I remove GST from a total price?

Base price = Total ÷ (1 + rate/100). For example, ₹11,800 that already includes 18% GST gives a base of ₹10,000 and ₹1,800 of GST.

Is GST calculated on the base price or the total?

GST is charged on the taxable (base) value. When a price is GST-inclusive, you first back out the base before working out the tax.

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GST Guide · India

How to calculate GST: add & remove GST

Q: What is the formula to add GST?

GST amount = Base price × GST rate ÷ 100. Total = Base price + GST amount. For example, ₹10,000 at 18% gives ₹1,800 GST and a ₹11,800 total.

There are really only two GST sums you'll ever need: adding GST to a base price, and removing GST from a price that already includes it. This guide covers both formulas with clear, worked examples at the current GST 2.0 rates.

The two formulas at a glance

Add GST (GST amount)Base × rate ÷ 100

Add GST (total)Base + GST amount

Remove GST (base)Total ÷ (1 + rate/100)

Remove GST (GST inside)Total − base

Adding GST to a price

Use this when you have a price before tax and want the final amount the customer pays.

Take the base price. Say a service costs ₹10,000 before GST.
Find the GST amount. At 18%: ₹10,000 × 18 ÷ 100 = ₹1,800.
Add it on. ₹10,000 + ₹1,800 = ₹11,800 total.

The same method works at any slab. At 5%, ₹2,000 × 5 ÷ 100 = ₹100 GST, so the total is ₹2,100. At 40%, ₹2,000 × 40 ÷ 100 = ₹800 GST, so the total is ₹2,800.

Removing GST from a total (reverse GST)

Use this when a price already includes GST — like an MRP or a quoted "all-in" figure — and you need to know the base and the tax hidden inside it. You can't just take a flat percentage off the total; you divide.

Take the GST-inclusive total. Say ₹11,800, which includes 18% GST.
Back out the base. ₹11,800 ÷ (1 + 18/100) = ₹11,800 ÷ 1.18 = ₹10,000.
The rest is GST. ₹11,800 − ₹10,000 = ₹1,800.

A quick check: a ₹1,050 price that includes 5% GST has a base of ₹1,050 ÷ 1.05 = ₹1,000 and ₹50 of GST inside it.

Splitting the GST: CGST, SGST or IGST

The total GST is the same whether the sale is within your state or across states — only the split changes. For a sale within the same state, the GST is divided equally into CGST and SGST. For a sale between two states, a single IGST is charged at the full rate.

So on that ₹1,800 of GST: an intra-state sale shows ₹900 CGST + ₹900 SGST, while an inter-state sale shows ₹1,800 IGST. We cover this fully in CGST vs SGST vs IGST explained.

Common mistakes to avoid

Subtracting a flat % from an inclusive price. Taking 18% off ₹11,800 gives the wrong base — you must divide by 1.18, not multiply by 0.82.
Using an old slab. Since GST 2.0 (22 September 2025), the 12% and 28% slabs are gone — see GST 2.0 explained.
Rounding too early. Round only the final figures, not each intermediate step.

These formulas are for standard GST calculation. The correct rate for any product or service depends on its HSN/SAC code — always confirm it from the official GST schedule at gst.gov.in or your accountant.

Frequently asked questions

What is the formula to add GST?

GST amount = Base × rate ÷ 100, and Total = Base + GST. For ₹10,000 at 18%, that's ₹1,800 GST and an ₹11,800 total.

How do I remove GST from a total?

Base = Total ÷ (1 + rate/100). For ₹11,800 including 18%, the base is ₹10,000 and the GST inside is ₹1,800.

Is GST charged on the base or the total?

On the taxable (base) value. If a price is GST-inclusive, back out the base first, then the remainder is the GST.

Does the calculation change for inter-state sales?

No — the total GST is identical. Only the split differs: CGST + SGST within a state, or a single IGST across states.

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