Tools
Free GST calculator with CGST, SGST and IGST split by state
Type the taxable value, pick the GST rate and choose where the seller and buyer are. The calculator adds the tax and shows whether it is CGST plus SGST or IGST.
In short
This free GST calculator from SimpleERP adds GST to a taxable value and splits it into CGST and SGST for a sale within a state, or IGST for a sale across states. It runs the same tax functions as a SimpleERP invoice.
How to use it
Four inputs, and the answer updates as you type.
Enter the taxable value
The price before GST, such as ₹10,000 for a steel rack order. If your price already includes GST, use the reverse GST calculator instead.
Pick the GST rate
5% and 18% cover most goods after the 2025 rate changes; 40% applies to a short list. 12% and 28% stay in the list for checking older invoices.
Choose the seller's and buyer's states
The seller's state is where you are registered. The buyer's state is the place of supply, usually where the goods are delivered.
Read the split
Same state shows CGST and SGST at half the rate each. Different states show IGST at the full rate. The total is the same either way.
Why does the split depend on place of supply?
GST is a tax on consumption, so it goes to the state where the goods or services are consumed. A sale inside one state is shared between the Centre and that state as CGST and SGST. A sale to another state is charged as IGST, collected by the Centre and passed to the consuming state.
- Seller in Tamil Nadu, buyer in Tamil Nadu: CGST 9% and SGST 9% on an 18% item.
- Seller in Tamil Nadu, buyer in Karnataka: IGST 18%.
- Union territories without a legislature, such as Chandigarh or Lakshadweep, charge UTGST in place of SGST.
- Charging the wrong one is not fixed by paying the right one later. You pay the correct tax and claim a refund of the wrong one, so get it right on the invoice.
Read more in place of supply explained.
Which GST rate should I pick?
The rate depends on the HSN code of the goods or the SAC code of the service, not on who the buyer is. Furniture under HSN 9403 is a common 18% example.
- Look up the HSN or SAC code first, then the rate notified for it.
- Rates changed in September 2025, when most 12% items moved to 5% and most 28% items moved to 18%.
- Rates change, so confirm the rate for your goods with your CA or the GST portal before you rely on it.
Illustration of the keyboard-first invoice editor with a focused line, live tax totals and shortcut hints.
Do this automatically in SimpleERP
On a SimpleERP invoice you never pick CGST or IGST by hand. The product reads your state from your GSTIN and the place of supply from the customer's address, then splits the tax on every line.
- Place of supply from the customer's state, changeable per invoice when goods go somewhere else.
- GST rate per product, with HSN printed on the line and an HSN summary on the invoice.
- The tax posts to the right ledger, so CGST, SGST and IGST payable are separate in the books.
- Amount in words printed on the invoice, in lakh and crore.
Illustration of GST tax invoice INV-2026-27-0213 to Ravi Stores with CGST 9% and SGST 9%, round off, a UPI QR code and the amount in words.
The maths
How it is calculated
GST is worked out on the taxable value, then split by where the sale happens.
- Tax = taxable value × rate ÷ 100.
- Within a state: CGST = taxable value × (rate ÷ 2) ÷ 100, and SGST (or UTGST) the same, so the two halves are always equal.
- Across states: IGST = the full tax.
- Invoice total = taxable value + tax.
- Each amount is rounded to the paisa, as on a SimpleERP invoice line.
Example
Worked example
Lakshmi Steel Furnitures in Coimbatore, Tamil Nadu, sells steel racks worth ₹10,000 at 18% GST.
| Buyer's state | CGST | SGST | IGST | Total |
|---|---|---|---|---|
| Tamil Nadu (33) | ₹900.00 | ₹900.00 | ₹11,800.00 | |
| Karnataka (29) | ₹1,800.00 | ₹11,800.00 |
Type 10000, pick 18% and switch the buyer between Tamil Nadu and Karnataka to see the calculator give the same figures.
Honest limits
What this calculator does not do
- Compensation cess on items that carry it is not added.
- Composition scheme dealers cannot charge GST on a bill of supply, so the split does not apply to them.
- Reverse charge, exports and SEZ supplies are outside this calculator; ask your CA how they apply to you.
FAQ
Questions, answered
How do I calculate GST on 10,000 at 18 percent?
Multiply 10,000 by 18 and divide by 100 to get ₹1,800 of GST, so the total is ₹11,800. Within one state that is CGST ₹900 and SGST ₹900; to another state it is IGST ₹1,800.
What is UTGST and when is it charged?
UTGST replaces SGST on a sale within Chandigarh, Ladakh, Lakshadweep, the Andaman and Nicobar Islands, or Dadra and Nagar Haveli and Daman and Diu, at the same half rate. Delhi and Puducherry have their own legislatures and charge SGST. The calculator labels the half for you.
When do I charge IGST instead of CGST and SGST?
When the seller's state and the place of supply are different. For goods that is usually where they are delivered. A Coimbatore seller delivering to Bengaluru charges IGST; delivering to Chennai, CGST and SGST.
Does the total change between CGST plus SGST and IGST?
No, apart from a paisa of rounding at most, since CGST and SGST are each rounded on their own. Only the heads change, which matters for which ledger the tax goes to and for the buyer's input tax credit.
Related
Keep reading
GST billing
Tax invoices with CGST, SGST or IGST by place of supply, HSN on every line and a UPI QR on the print.
Read morePlace of supply
Where GST treats a supply as happening, which decides CGST and SGST or IGST.
Read moreGST invoice format
A GST tax invoice format with every rule 46 field, as a free Excel, Word and PDF download.
Read more
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