GST Calculator
Add GST to a price, or work out how much GST is already inside one. Pick a rate, type an amount, and the base, the tax and the CGST/SGST/IGST split update as you go.
Base amount (before GST)
Total GST
Invoice total
Intra-state supply
- CGST
- SGST / UTGST
Supplier and place of supply in the same state or UT. The rate is split down the middle between the Centre and the state.
Inter-state supply
- IGST
- CGST + SGST
- Not applicable
Supplier and place of supply in different states, or an import. The full rate is charged as one integrated levy.
The customer pays the same total either way — only the heads change. Which one applies is decided by the place of supply, and the supplier's state is the first two digits of their GSTIN. Look up a state code.
The two GST formulas, spelled out
Every GST calculation is one of two problems: you have a price without tax and need to add it, or you have a price with tax baked in and need to pull it back out. They are not the same sum, and treating them as the same sum is the single most common GST arithmetic error on invoices.
Adding GST (exclusive → inclusive)
GST = amount × rate ÷ 100
Total = amount + GST
A consultant bills ₹10,000 for services taxed at 18%. GST is 10,000 × 18 ÷ 100 = ₹1,800. The invoice total is ₹11,800. Within one state that ₹1,800 is shown as ₹900 CGST plus ₹900 SGST; across states it is ₹1,800 IGST on a single line.
Removing GST (inclusive → exclusive)
Base = amount × 100 ÷ (100 + rate)
GST = amount − base
A shop sells an item at a shelf price of ₹11,800 including 18% GST. The base is 11,800 × 100 ÷ 118 = ₹10,000, so the GST inside the price is ₹1,800. Taking 18% of ₹11,800 instead gives ₹2,124 — over by ₹324, and enough to throw out a whole month's output tax.
If this is the direction you need, the reverse GST calculator does only this, with a worked table at every rate.
CGST + SGST or IGST: which one you charge
GST is one tax collected under three heads. The total the customer pays never changes; what changes is how the money is divided between the Centre and the states, and that is decided entirely by where the supply lands.
| Scenario | Heads charged | On ₹10,000 at 18% |
|---|---|---|
| Supplier in Maharashtra, customer in Maharashtra | CGST + SGST | ₹900 + ₹900 = ₹1,800 |
| Supplier in Maharashtra, customer in Karnataka | IGST | ₹1,800 |
| Supplier in Chandigarh, customer in Chandigarh | CGST + UTGST | ₹900 + ₹900 = ₹1,800 |
| Import of goods or services into India | IGST | ₹1,800 (plus customs duties on goods) |
| Supply to or from an SEZ unit | IGST — treated as inter-state | ₹1,800, or zero-rated where the supply qualifies |
Getting this wrong is expensive in a specific way: if you charge CGST and SGST on what was actually an inter-state supply, your customer cannot claim the credit in their own state and you have to pay IGST afresh before reclaiming the wrongly paid tax. Check the counterparty's state before you raise the invoice, not after — the state code is the first two characters of their GSTIN, and the full state code list explains the tricky ones.
Which rate applies
The GST 2.0 rationalisation took effect on 22 September 2025 and collapsed the old four-slab structure into essentially two, plus a de-merit rate at the top. These are the bands you will be picking from on a current invoice.
| Rate | Status | Broadly what sits here |
|---|---|---|
| 0% | Current | Exempt and nil-rated supplies. The exempt list was widened by the reform, with everyday food items such as milk, paneer and roti moved into it. |
| 0.25% | Current, special | Rough and semi-processed diamonds and other precious stones. A long-standing carve-out, untouched by the reform. |
| 3% | Current, special | Gold, silver, platinum and articles of jewellery. Also unchanged by the reform. |
| 5% | Current, main slab | The lower of the two main slabs. It absorbed the overwhelming majority of items that used to sit at 12%. |
| 12% | Phased out | Removed for most items from 22 September 2025. Still needed for invoices, credit notes and amendments relating to earlier periods. |
| 18% | Current, standard slab | The standard rate for most goods and services, and where the bulk of the old 28% band landed. |
| 28% | Phased out | Removed for most items. Its luxury and sin-goods residue moved to 40% rather than down to 18%. |
| 40% | Current, de-merit | A narrow list of luxury and sin goods — aerated beverages and similar — that previously carried 28% plus compensation cess. |
When reverse charge flips who pays
Normally the supplier collects GST from the customer and remits it. Under the reverse charge mechanism the supplier issues an invoice with no GST on it and the registered recipient pays the tax straight to the government instead. The arithmetic on this page is unchanged — ₹10,000 at 18% is still ₹1,800 — but the ₹1,800 comes out of the buyer's pocket and goes on the buyer's return.
- Notified supplies. A published list of goods and services always attracts reverse charge regardless of who the supplier is — goods transport agency services, legal services from an advocate, sponsorship, and director services are the ones most businesses meet.
- Certain purchases from unregistered suppliers. A narrow, notified set of cases where a registered buyer takes on the tax because the seller is outside the GST net.
- Pay in cash, then claim credit. Reverse charge liability cannot be discharged by offsetting input tax credit. You pay it in cash and claim the credit separately, subject to the usual eligibility rules — so it is a cash-flow event even when it is ultimately tax-neutral.
- Self-invoicing. Where the supplier is unregistered, the recipient raises a self-invoice for the supply. Skipping this is one of the most routine reverse-charge audit findings.
The full mechanics, including how reverse charge interacts with credit, are in the reverse charge mechanism explained. For what you can and cannot claim on the other side, read the input tax credit rules.
The number that actually costs you money is the GSTIN
Getting the arithmetic right is the easy half. The expensive mistake is paying an invoice from a supplier whose registration was cancelled, or whose GSTIN never existed — because the input tax credit on that invoice will not survive reconciliation against GSTR-2B, and the amount at stake is exactly the GST you just calculated. Check the counterparty before you pay, not at the year-end.
Related reading: GSTR-2B and the Invoice Management System, the e-invoicing threshold in 2026, and the composition scheme limit if your supplier cannot charge you GST at all.
Related free tools
GST number search
Look a GSTIN up against the government register — legal name, status, jurisdiction and return filing history.
GSTIN validator
Check any GST number’s format and check digit offline, with a character-by-character breakdown.
GST state code finder
Search all GST state codes by number or state name, or paste a GSTIN to get its state.