GST Calculator
Add GST to a base amount or extract it from a GST-inclusive total — with the CGST, SGST and IGST split worked out instantly.
Your amount is exclusive of GST — we add it on top.
Total GST
₹18,000.00
- Base amount
- ₹1,00,000.00
- CGST @ 9%
- ₹9,000.00
- SGST / UTGST @ 9%
- ₹9,000.00
- Total (incl. GST)
- ₹1,18,000.00
Indicative only. The rate applicable to your goods or services depends on their HSN/SAC classification. Confirm the correct rate before invoicing.
The maths behind the number.
Adding GST is straightforward: multiply the base value by the rate and add it on. A base of ₹1,00,000 at 18% carries ₹18,000 of GST, giving an invoice value of ₹1,18,000.
Working backwards is where people slip. If someone quotes you ₹1,18,000 “inclusive of GST”, the tax is not 18% of ₹1,18,000. You divide by 1.18 to recover the base of ₹1,00,000, and the GST component is the difference — ₹18,000. Applying the rate to the inclusive figure overstates the tax every time.
The split then depends on where the supply moves. Within one state, the tax is shared equally between the Centre and the State as CGST and SGST — 18% becomes 9% plus 9%. Across states, a single IGST is charged at the full 18%. The amount your customer pays is identical; what changes is which government receives it and how it flows through your returns.
One caveat worth repeating: this tool does the arithmetic, not the classification. The rate applicable to your supply comes from its HSN or SAC code, and picking the wrong one is a common, expensive error that surfaces later as short payment, interest and penalty.
Frequently asked.
How do I calculate GST on an amount?+
To add GST, multiply the base amount by the GST rate and add it to the base — so ₹1,00,000 at 18% gives ₹18,000 of GST and a total of ₹1,18,000. To work backwards from a GST-inclusive figure, divide the total by (1 + rate ÷ 100). The calculator above does both.
What is the formula to remove GST from a total amount?+
Base amount = total ÷ (1 + GST rate ÷ 100). For a ₹1,18,000 total at 18%, the base is ₹1,18,000 ÷ 1.18 = ₹1,00,000, and the GST component is ₹18,000. This is often called a reverse GST calculation.
What is the difference between CGST, SGST and IGST?+
For a supply within the same state (intra-state), the tax is split equally between Central GST and State GST — 18% becomes 9% CGST plus 9% SGST. For a supply between states (inter-state), a single Integrated GST is charged at the full rate. The total tax is the same either way; only the split differs.
What are the GST rate slabs in India?+
The main slabs are 5%, 12%, 18% and 28%, with special rates of 0.25% and 3% for items such as rough diamonds and gold. Many essential goods and services are nil-rated or exempt. The rate that applies to you depends on the HSN code for goods or the SAC code for services.
Which GST rate applies to my product or service?+
It depends on the classification of what you supply under the HSN (goods) or SAC (services) schedule, not on your industry generally. Most services default to 18%, but there are many exceptions. Getting classification wrong causes short payment, interest and disputes, so it is worth confirming before you invoice.
Is GST calculated on the amount before or after discount?+
GST is charged on the transaction value after any discount shown on the face of the invoice. Discounts agreed after supply can only be excluded if they were agreed before or at the time of supply, are linked to the relevant invoices, and the buyer reverses the related input tax credit.
Do I need GST registration to charge GST?+
Yes. Only a person registered under GST may collect GST and issue a tax invoice. Registration is generally required once aggregate turnover crosses ₹40 lakh for goods or ₹20 lakh for services (lower in special-category states), and is compulsory from the first rupee in certain cases such as inter-state supply of goods and e-commerce.
Is this GST calculator accurate for filing my returns?+
It is accurate for the arithmetic, and useful for quoting and invoicing. It cannot decide the correct rate for your supply or handle reverse charge, exemptions and input tax credit, all of which affect what you actually pay. Treat it as a quick check rather than a substitute for advice.
Need a GST number, or help filing?
We handle GST registration end to end and run monthly and annual filings so your input tax credit is protected and nothing lapses.