GST Calculator
Add or remove GST using the common Indian slabs — 5%, 12%, 18%, and 28%. This free online GST calculator gives you the base amount, GST, and total instantly, with no sign-up.
Enter a base price to add GST and see the final amount, or enter a GST-inclusive price to work out the pre-tax base and the GST portion — handy for invoicing or checking a bill. Every result also shows the CGST and SGST halves, which is what an intra-state invoice has to list separately.
GST rate
How to calculate GST
- Choose add or remove GST. Pick "Add GST" if your figure is the pre-tax base price, or "Remove GST" if it already includes tax and you need the base amount back.
- Enter the amount. Type the price into the amount field. You can paste a figure straight from an invoice — commas and the ₹ symbol are handled.
- Select the GST rate. Choose one of the standard slabs — 5%, 12%, 18%, or 28% — or pick Custom for a rate outside them, such as the 0.25% on rough gemstones or the 3% on gold.
- Read the breakdown. The base amount, GST, and total appear instantly, along with the CGST and SGST halves for an intra-state invoice.
The GST formulas
Adding GST. Multiply the base price by the rate over 100, then add it back: a ₹1,000 base at 18% gives ₹180 GST and a ₹1,180 total.
Removing GST (reverse GST). Divide the inclusive amount by 1 plus the rate over 100 — ₹1,180 ÷ 1.18 = a ₹1,000 base, leaving ₹180 GST. Subtracting 18% from the total instead is the usual mistake, and it under-reports the base by about ₹18 on this example, because the 18% was charged on the base and not on the total.
CGST, SGST and IGST. A sale within one state splits the GST evenly between the centre and the state, so 18% is listed as 9% CGST plus 9% SGST. A sale across state lines carries the same 18% as a single IGST line. The total the customer pays is identical either way — only the split on the invoice changes.
Frequently asked questions
Which GST slabs does the calculator support?
The common Indian GST rates — 5%, 12%, 18%, and 28% — are built in as quick-select options. There's also a Custom field for other rates, such as the 0.25% on rough gemstones and 3% on gold.
Can I remove GST from a GST-inclusive price?
Yes. Switch to "remove GST" mode, enter the final price, and the calculator backs out the base price and GST amount. This is called reverse GST, and it's the calculation you need when a receipt shows only the total.
How is GST added to a price calculated?
GST amount = base price × (GST rate ÷ 100), and the final price is the base price plus that GST amount. At 18%, a ₹1,000 base becomes ₹180 GST and ₹1,180 total.
How do I work out GST backwards from the total?
Divide the inclusive amount by (1 + rate ÷ 100) to get the base. At 18%, a ₹1,180 total divided by 1.18 gives a ₹1,000 base and ₹180 GST. Dividing by the rate alone is the common mistake and gives the wrong answer.
What are CGST and SGST, and how are they split?
On a sale within a single state, GST is collected half by the centre (CGST) and half by the state (SGST). An 18% rate is therefore 9% CGST plus 9% SGST. The calculator shows both halves under the result. On an inter-state sale the same total is charged as a single IGST line instead.
Is this GST calculator free, and are my figures private?
It's completely free with no sign-up. The calculation runs entirely in your browser, so the amounts you enter are never sent to a server.