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India finance

GST Calculator

Add GST to a base price or extract it from an inclusive one, at any slab, with the CGST/SGST split shown.

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Quick answer

Adding 18% GST to ₹1,000 gives ₹1,180. Removing it from an inclusive ₹1,180: base = amount ÷ 1.18 = ₹1,000, not amount minus 18%, which is the classic error and understates the base by ₹32.40 on this example.

Price including GST
₹1,180.00
GST amount
₹180.00
CGST + SGST
₹90.00 + ₹90.00
Split equally on intra-state sales; inter-state levies IGST instead.

Formulas last verified 2026-10-10. Results are estimates, not financial advice. How we calculate.

The two directions, and the one mistake

Adding: total = base × (1 + rate)
Removing: base = total ÷ (1 + rate)

Adding is intuitive. Removing is where invoices go wrong: the GST inside a price was computed on the base, so recovering the base must divide, not subtract. The size of the error grows with the rate:

Inclusive priceSlabCorrect base (÷)Wrong base (−%)Error
₹1,0505%₹1,000.00₹997.50₹2.50
₹1,18018%₹1,000.00₹967.60₹32.40
₹1,40040%₹1,000.00₹840.00₹160.00

On a freelancer's ₹5 lakh of annual inclusive billing at 18%, the subtraction error misstates income by over ₹16,000, enough to matter at filing time.

Who uses which direction

  • Freelancers and small businesses, quoting ex-GST and invoicing with GST added; or receiving inclusive amounts and needing the taxable value for returns (the remove direction).
  • Shoppers comparing B2B and retail prices, putting an ex-GST quote and an inclusive price on the same footing.
  • Accounting cross-checks, verifying that an invoice's CGST + SGST halves sum to the slab, and that the base × rate reproduces the tax line to the paisa.

Percentages behaving badly

The divide-don't-subtract rule is one instance of a general trap: percentages are not symmetric. Adding 18% and then subtracting 18% does not return the original (it lands 3.24% low), the same way a 10% gain then a 10% loss nets to 99%, the bases differ. The percentage calculator covers the general cases, and the discount calculator shows the same effect in stacked sale offers. For the payroll-side tax rules, see the HRA exemption page.

Frequently asked questions

How do I remove GST from a price that includes it?

Divide by (1 + rate), never subtract the percentage. A ₹1,180 bill at 18% GST: base = 1180 ÷ 1.18 = ₹1,000, GST = ₹180. The wrong way, 1180 minus 18%, gives ₹967.60, understating the base by ₹32.40, because the 18% in the price was charged on the base, not on the total.

What are CGST, SGST and IGST?

The same tax, split by geography. Within a state, GST divides equally into central (CGST) and state (SGST) halves, an 18% intra-state sale is 9% + 9%. Across states, the whole amount is levied as integrated GST (IGST). The buyer's total is identical either way; only the government account receiving it differs.

What are the GST slabs?

Since 22 September 2025 the main rates are 5% and 18%, with 40% for luxury and sin goods, 0% for many essentials and special rates for a few categories (3% on gold and silver, 0.25% on rough diamonds). The old 12% and 28% slabs were folded into these; 28% survives only on some tobacco products until the compensation cess ends. Most services sit at 18%, which is why it is the default here. For an older bill, pick 12% or 28%. Classification changes at GST Council meetings, so for invoicing confirm the current rate for your specific item.

Why does my invoice show GST but my quote did not?

B2B quotes are conventionally ex-GST (buyers reclaim it as input credit, so it is not a cost to them); consumer prices are legally required to be GST-inclusive. When comparing quotes, always establish which convention is in use first, an 18% surprise at invoice time is the classic result of not asking.

Can businesses get GST back?

GST-registered businesses offset the GST they pay on inputs against the GST they collect on sales (input tax credit), so GST flows through them rather than costing them, the burden lands on the end consumer. That is the design of the tax, and why the add/remove arithmetic on this page matters mostly for pricing and invoicing correctness.

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