GST calculator, with the split you actually have to write on the invoice.
Enter an amount and a rate. Get the base value, the tax, and whether it is CGST and SGST or IGST — inclusive or exclusive, both ways round.
Breakdown
- Amount
- ₹10,000.00
- CGST @ 9%
- ₹900.00
- SGST @ 9%
- ₹900.00
- Total
- ₹11,800.00
Total GST of ₹1,800.00 at 18%, split equally into CGST and SGST.
Most GST arithmetic is simple until two things happen at once. The first is a price quoted inclusive of tax, which means working backwards from the total rather than forwards from the base — and dividing by 1.18 is not the same as taking 18% off, which is the mistake that quietly costs a few hundred rupees on every such invoice.
The second is the split. The same 18% is one line as IGST when the goods cross a state border and two lines of 9% as CGST and SGST when they do not. Getting that wrong does not change what the customer pays, but it does change what they can claim, which means the invoice comes back.
This calculator does both. Enter the amount, pick the rate, say whether the figure already includes tax and whether the supply is within the state or across one, and it returns the base value, the tax split line by line, and the total.
The formula
- Tax on an exclusive amount
GST = Amount × Rate ÷ 100- Base from an inclusive amount
Base = Amount × 100 ÷ (100 + Rate)- Within the same state
CGST = SGST = GST ÷ 2- Across states
IGST = GST
Inclusive and exclusive are not the same sum
If a price is quoted exclusive of GST, the tax is added on top: ₹10,000 at 18% becomes ₹1,800 of tax and ₹11,800 payable. Straightforward.
If the same ₹11,800 is quoted inclusive, the tax already sits inside it, and the base is not ₹11,800 less 18%. It is ₹11,800 × 100 ÷ 118, which is ₹10,000 — and the tax is ₹1,800. Taking 18% off ₹11,800 would have given ₹9,676, understating the base by ₹324 and the tax with it. On one invoice it is an irritation. Across a year of quoting inclusive prices it is a reconciliation nobody enjoys.
CGST and SGST, or IGST
Which split applies depends on the place of supply, not on where your office is. When the supplier and the place of supply are in the same state, the tax divides equally into central and state components — 18% becomes 9% CGST and 9% SGST. When they are in different states it is a single line of IGST at the full rate.
The total is identical either way, which is why the error is easy to miss internally and easy for the recipient to catch. Their input credit is claimed against specific heads, so an invoice carrying the wrong ones has to be revised before they can use it.
Where this fits in a manufacturing business
A calculator is useful for a quotation or a one-off check. It stops being the right tool the moment invoices are being raised in volume, because the rate, the place of supply and the amount are all already recorded elsewhere — on the sales order, in the customer master, on the dispatch. Re-entering them into a calculator to produce a figure that is then typed into an invoice is three chances to introduce an error where there should be none.
In a system where the invoice is generated from the dispatch, the split is decided by data the business already holds rather than by whoever is filling in the form.
Questions people ask.
How do I calculate GST on an amount?
If the amount excludes tax, multiply it by the rate and divide by 100 — ₹10,000 at 18% gives ₹1,800. If the amount already includes tax, work backwards instead: base = amount × 100 ÷ (100 + rate), so ₹11,800 at 18% has a base of ₹10,000 and ₹1,800 of tax.
When is it CGST and SGST instead of IGST?
When the supplier and the place of supply are in the same state, the tax splits equally into CGST and SGST — 18% becomes 9% and 9%. When they are in different states it is a single IGST line at the full rate. The total payable is the same either way.
How do I remove GST from a total that already includes it?
Divide rather than subtract. Base = total × 100 ÷ (100 + rate). Subtracting the rate from the total gives a smaller, wrong answer, because the rate applies to the base and not to the total.
What are the GST rates in India?
The main slabs are 5%, 12%, 18% and 28%, with 0% for exempt items and special rates for a few categories. Which one applies depends on the HSN classification of what you are supplying, so check the classification rather than assuming the rate.
Is this calculator free to use?
Yes. It runs entirely in your browser, needs no sign-up, and nothing you type is sent anywhere.
Other free tools
Doing this for every item, every day?
A calculator is the right tool once. When it is every item in the store, it belongs in the system that already knows the numbers.