Add GST to a base price or strip it out of an inclusive price — with the CGST/SGST/IGST split done for you.
How GST is calculated
GST is a percentage of the taxable value. There are only two calculations you ever need, and the calculator above does both:
Adding GST to a base price (exclusive → inclusive)
GST amount = base price × rate ÷ 100. Example at 18%: a service billed at ₹10,000 attracts GST of ₹10,000 × 18 ÷ 100 = ₹1,800, so the invoice total is ₹11,800.
Removing GST from an inclusive price (inclusive → exclusive)
Base price = inclusive price × 100 ÷ (100 + rate). Example at 18%: a product sold at an all-inclusive ₹11,800 has a base price of ₹11,800 × 100 ÷ 118 = ₹10,000, and the GST inside it is ₹1,800.
The classic mistake is removing GST by simply deducting 18% of the inclusive price — ₹11,800 − ₹2,124 = ₹9,676, which is wrong. You must divide by 1.18, not multiply by 0.82. On a ₹10 lakh contract, that error misstates the taxable value by over ₹27,000.
GST rate slabs
| Rate | Typically applies to |
|---|---|
| 0% | Exempt and nil-rated supplies — many unprocessed food items and other essentials. |
| 0.25% | Rough precious and semi-precious stones. |
| 3% | Gold, silver and articles of jewellery. |
| 5% | Mass-consumption goods and select services. |
| 12% | Intermediate-rate goods and services. |
| 18% | The default rate for most services and a wide range of goods. |
| 28% | Luxury and demerit goods, some with additional cess on top. |
Rates are set per item by the GST Council and change over time — always confirm the current rate for your specific goods or services against an official notification before invoicing.
CGST + SGST vs IGST: which split applies?
The total GST rate is the same either way; what changes is who collects it, and it depends on whether the supply crosses a state border:
- Intra-state supply (seller and place of supply in the same state): the rate splits equally into CGST (Central GST) and SGST (State GST). An 18% invoice within Maharashtra shows CGST 9% + SGST 9% — on ₹10,000, that is ₹900 + ₹900.
- Inter-state supply (different states, or imports): the whole rate is charged as IGST (Integrated GST). The same ₹10,000 invoice from Maharashtra to Karnataka shows IGST 18% = ₹1,800 in a single line.
How do you know which states are involved? The first two digits of each party’s GSTIN. A supplier GSTIN starting 27 billing a customer GSTIN starting 29 is Maharashtra → Karnataka, hence IGST. Decode any prefix with the GST state code list, and check a counterparty’s registration with the GST number check before relying on it. If a supplier charges you CGST + SGST for a state where they hold no registration, that is one of the fraud patterns covered under GST verification.
Worked example, end to end
You are a Delhi consultant (GSTIN starting 07) billing ₹1,50,000 for a project to a Gujarat client (GSTIN starting 24) at 18%. Different states → IGST. Tax = ₹1,50,000 × 18 ÷ 100 = ₹27,000; invoice total ₹1,77,000. Had the client been in Delhi too, the identical ₹27,000 would instead appear as CGST ₹13,500 + SGST ₹13,500. Your registered client can generally claim that tax as input tax credit — one more reason they will verify your GSTIN, just as you should verify theirs. New to these numbers entirely? Start with what is a GSTIN or how to get a GST number.
GST calculator FAQs
How do I calculate GST at 18% quickly?
To add: multiply the base by 0.18 for the tax, or by 1.18 for the total. To remove: divide the inclusive amount by 1.18 to get the base. The calculator above does this for every slab and shows the CGST/SGST/IGST split.
What is the formula to remove GST from an MRP or inclusive price?
Base = inclusive × 100 ÷ (100 + rate). At 12%, an inclusive ₹5,600 breaks into base ₹5,000 + GST ₹600. Never subtract the rate percentage directly from the inclusive price — that overstates the tax.
Is the total tax different under CGST+SGST versus IGST?
No. The buyer pays the same total either way — 18% is 18%. The split only determines whether the tax goes to the Centre and the state in halves (intra-state) or as one integrated amount (inter-state).
Which GST rate should I use for my product?
Rates are fixed per HSN/SAC classification by the GST Council, and this page cannot decide your classification for you. Check the current rate notification for your item or ask a tax professional; then use the calculator for the arithmetic.
Can I add GST to an invoice if I’m not registered?
No — only registered taxpayers with an active GSTIN may collect GST. If your turnover has crossed the threshold, see how to get a GST number; if a supplier is charging you GST, confirm their registration with GST verification.