GST Calculator

Goods and Services Tax (GST) is a single indirect tax levied on the supply of goods and services in India, replacing multiple earlier taxes like VAT, service tax, and excise duty. GST is charged as a percentage of the base (taxable) value of the goods or service, at slabs set by the GST Council.

Adding GST: GST Amount = Base Amount × (Rate ÷ 100); Total Amount = Base Amount + GST Amount. Removing GST (when you have a GST-inclusive price and need the base): Base Amount = Inclusive Amount ÷ (1 + Rate ÷ 100); GST Amount = Inclusive Amount − Base Amount.

Worked example (adding GST): a base amount of ₹10,000 at 18% GST adds ₹1,800, giving a total of ₹11,800. For an intra-state sale, this splits into ₹900 CGST + ₹900 SGST; for an inter-state sale, it's ₹1,800 IGST.

Worked example (removing GST): a GST-inclusive price of ₹11,800 at 18% GST has a base amount of ₹11,800 ÷ 1.18 = ₹10,000, with ₹1,800 as the GST component — useful when you're given a final MRP and need to back out the taxable value.

1. Applying the GST rate on an inclusive amount as if it were exclusive. If a price already includes GST, multiplying it again by the rate overstates the tax — use the "remove GST" division method instead of a second multiplication.

2. Mixing up CGST/SGST with IGST. Charging CGST+SGST on an inter-state sale (or IGST on an intra-state sale) is a common invoicing error — the split depends on whether the buyer and seller are in the same state or different states.

3. Using the wrong slab rate for the product category. GST rates vary significantly by HSN/SAC classification — always verify the correct rate for your specific goods or service rather than assuming a "standard" 18%.

4. Still invoicing at the old 12% or 28% rate. Since GST 2.0 took effect on 22 September 2025, the 12% and 28% slabs no longer apply to most goods — an invoice raised at either rate after that date is generally treated as incorrect under Section 122 of the CGST Act and should be checked against the current 5%/18%/40% structure and your billing software's updated rate master.

5. Forgetting the 40% slab on luxury and sin goods. A few categories — tobacco, pan masala, aerated drinks, high-end vehicles — now sit above the standard 18% rate at 40% rather than the old 28%-plus-cess structure; using 28% for these post-reform understates the tax due.

6. Not reconciling input tax credit (ITC) correctly. Businesses often miscalculate net GST payable by ignoring eligible input tax credit on purchases — GST payable to the government is output GST minus eligible input GST, not the full output GST amount.