Whether you are adding GST to a quote, backing it out of an MRP, or checking whether a supplier's invoice split CGST and SGST correctly, the arithmetic is simple but the mistakes are expensive. This GST calculator does it live: pick a rate, type an amount, and see the taxable value, CGST, SGST or IGST, and the total — in add-GST (exclusive) or remove-GST (inclusive) mode, with a composition-scheme comparison for small dealers. It reflects the slab structure in force since 22 September 2025.
The GST slabs in 2026
The GST Council's September 2025 rationalisation — called GST 2.0, and often "GST 3.0 reforms" in the press — collapsed the four main slabs into two, plus a demerit rate:
| Rate | What falls here |
|---|---|
| 0% | Unbranded food grains, fresh produce, milk, education, health services, most books |
| 3% | Gold, silver, precious stones (0.25% on rough diamonds) |
| 5% | Most packaged food, footwear and apparel up to the threshold, restaurants without ITC, hotel rooms ≤ ₹7,500, small cars, cement's former 28% moved to 18% |
| 18% | The default for most goods and services — electronics, furniture, telecom, professional services, larger vehicles |
| 40% | Tobacco, pan masala, aerated and sugary drinks, luxury cars and the former "sin" list |
What moved where, item by item, is in GST 2.0 rate changes. Use the custom-rate field for invoices dated before the change (12% or 28%) or for rare rates like 1.5% and 7.5%.
The formulas
- Add GST: tax = base × rate; total = base × (1 + rate). ₹10,000 at 18% → ₹1,800 tax, ₹11,800 total.
- Remove GST (inclusive price): base = total ÷ (1 + rate); tax = total − base. ₹11,800 inclusive at 18% → base ₹10,000, tax ₹1,800. A common error is computing 18% of ₹11,800 (₹2,124), which overstates the tax.
- Intra-state supplies split the rate equally: 18% = 9% CGST + 9% SGST. Inter-state supplies charge the full rate as IGST. The place of supply — usually the buyer's location for goods — decides which.
Worked examples by rate, including MRP reverse calculations, are in How to calculate GST from MRP.
How to use the calculator
- Choose Add GST if you know the base price, or Remove GST if you have an inclusive price or MRP.
- Tap a slab button or enter a custom rate.
- Switch to IGST for inter-state sales; the CGST/SGST split appears otherwise.
- Optionally open the composition comparison to see what a composition dealer would pay on the same turnover (1% for traders and manufacturers, 5% for restaurants, 6% for other service providers).
- Copy the figures into a GST invoice or a price tag.
Composition vs regular: a quick sanity check
A trader with ₹80 lakh turnover pays 1% (₹80,000) under composition and cannot collect GST from customers or claim input credit. Under the regular scheme they collect 18% on sales and set off 18% on purchases, so the net tax is 18% of value added. Composition wins when margins are thin and inputs are tax-free; regular wins when customers are businesses that want ITC. The full decision is in the GST composition scheme guide.
Common mistakes
- Applying the slab to the wrong base: discounts shown on the invoice reduce the taxable value before GST.
- Rounding per line: Section 170 rounds the invoice total, not each line.
- Charging IGST to a customer in your own state because their billing address is elsewhere — place of supply for goods is where delivery ends.
- Forgetting cess on aerated drinks, coal or cars where compensation cess still applies in addition to the slab.
- Using old rates for supplies after 22 September 2025 — the rate on the date of supply governs.
Related tools
- HSN/SAC finder — find the code and rate for your product.
- GST invoice generator — put the numbers on a compliant invoice.
- Discount calculator — discounts before or after tax.
- Profit margin calculator — margins on tax-exclusive prices.
- GST filing calendar — when the collected tax is due.