GST Calculator

How this is worked out

There is no single GST rate, so this calculator asks which slab applies instead of assuming one. Since 22 September 2025 the slabs are nil, 5%, 18% and 40%, with 3% on precious metals and jewellery and 0.25% on rough diamonds alongside them. Pan masala and tobacco stay at 28% with compensation cess pending a separate notification.

Adding GST multiplies by the rate. ₹1,000 at 18% is ₹180 of GST and ₹1,180 to pay.

Taking GST back out of an inclusive price is a division, not a subtraction:

taxable value = inclusive price ÷ (1 + rate)

₹1,180 contains ₹180 of GST. Subtract 18% instead and you get ₹967.60 — ₹32.40 short — because the ₹180 is 18% of the taxable value but only 15.25% of the inclusive price. This is the direction most people in India need, since a retail price already includes GST by law.

Then the split. Within one state the rate halves: 18% becomes 9% CGST and 9% SGST, ₹90 each. Across state lines the whole 18% is IGST, ₹180. The customer pays ₹1,180 either way, which is exactly why this is the thing invoices get wrong. The place of supply decides it, not the billing address.

A worked example

Four slabs, not one rate

The 56th GST Council meeting replaced the old 5/12/18/28 structure with nil, 5%, 18% and 40%, effective 22 September 2025. Nil covers unpacked food grains, fresh produce, milk, and most healthcare and education services. 5% covers packaged food, medicines, renewable energy equipment and economy air travel. 18% is the standard rate — electronics, processed food, most manufactured goods and most services. 40% is for luxury and sin goods: motorcycles over 350cc, yachts, carbonated drinks, gambling.

Three rates sit outside that list. Precious metals and jewellery are at 3% and rough diamonds at 0.25%, both unchanged by the reform. Pan masala and tobacco products remain at 28% plus compensation cess, and that one is not settled — it is held there pending a separate notification, so it is the figure on this page most likely to move.

The practical effect is that any rate table, quote or template written before 22 September 2025 may carry a slab that no longer exists. 12% is gone, and 28% survives only for the two categories above. If a supplier is still billing you at 12%, that is worth a question rather than an assumption.

CGST and SGST, or IGST: same total, different heads

A supply within one state splits the rate equally between the centre and the state. At 18% on ₹1,000 that is ₹90 of CGST and ₹90 of SGST. A supply across state lines does not split at all: the full 18%, ₹180, is IGST. The customer pays ₹1,180 in both cases.

Because the money is identical, nothing at the point of sale catches the mistake. The error surfaces later and somewhere else — in the recipient’s input-credit claim, where IGST claimed against a same-state supply does not match what the supplier reported. Fixing it means a credit note and a revised invoice, usually after someone else has already found it.

What decides it is the place of supply, not the billing address. Those are frequently different: a customer with a registered office in one state can take delivery in another, and it is the place of supply that governs. The first two digits of a GSTIN are the state code, which is why comparing the supplier’s code against the place of supply is the check worth doing before the invoice goes out.

MRP already includes GST, so extraction is the everyday job

Retail prices in India are GST-inclusive by law. The printed MRP is what you pay, and the tax is inside it. So the common operation is not adding GST to a price — it is pulling the taxable value back out of one, for an expense claim, a reimbursement, a books entry, or an input-credit check.

That is the operation this page exists for, because it is a division and people subtract. At 18%, subtracting gives ₹967.60 out of ₹1,180 instead of ₹1,000. The gap is about 2.75% of the total at that slab and it grows with the rate, which is enough to break a reconciliation without looking obviously wrong on a single line.

Business-to-business quotes are the exception, and the source of most arguments. A quote may legitimately be written "plus GST", so ₹1,00,000 becomes ₹1,18,000 on the invoice. If a quote does not say which it is, ask before you approve it.

Below the threshold you charge nothing and issue a bill of supply

Registration becomes compulsory at ₹40 lakh of annual aggregate turnover for a supplier of goods and ₹20 lakh for a supplier of services. In the special-category states those are halved, to ₹20 lakh and ₹10 lakh. The test is aggregate turnover, not profit, so a business with thin margins can cross it comfortably.

Below the threshold you are not registered, you do not charge GST, and you must not put a GST amount on a bill. What you issue is a bill of supply rather than a tax invoice — a different document with different contents, and the distinction matters to a registered customer, who can claim no input credit against it.

Registering voluntarily is a real option and the maths depends entirely on who buys from you. Selling to registered businesses, the GST you charge costs them nothing because they reclaim it, while you start reclaiming the GST on your own costs. Selling to consumers, registration means either raising the price by the slab or absorbing it.

Assumptions and sources

GST slabs

Nil, 5%, 18% and 40% following the 56th GST Council meeting, effective 22 September 2025, with 3% on precious metals and jewellery and 0.25% on rough diamonds. The 12% slab is withdrawn. checked 2026-09

Pan masala and tobacco

Retained at 28% plus compensation cess pending a separate notification — the one part of the new structure that is not settled. checked 2026-09

CGST, SGST and IGST

Intra-state supply splits the rate equally into CGST and SGST; inter-state supply is IGST at the full rate. The total is the same either way. checked 2026-09

Registration thresholds

₹40 lakh of annual aggregate turnover for goods, ₹20 lakh for services; ₹20 lakh and ₹10 lakh in the special-category states. checked 2026-09

Extraction formula

taxable value = inclusive price ÷ (1 + rate). The round trip is verified in tools/test/payroll.mjs.

Not included

Compensation cess, the composition scheme, reverse charge, and which HSN or SAC code your supply falls under — all of which can change what you actually pay.