How the GST calculator works
GST is charged on the taxable value of a supply: the price after any discount shown on the invoice, before tax. The calculator uses two simple formulas.
- Adding GST (price excludes GST): GST = taxable value × rate ÷ 100, and total = taxable value + GST.
- Removing GST (price includes GST): taxable value = total × 100 ÷ (100 + rate), and GST = total − taxable value.
When the supplier and the place of supply are in the same state, the GST is split equally into Central GST (CGST) and State GST (SGST), or Union Territory GST (UTGST) in UTs without a legislature. When they are in different states, the whole amount is Integrated GST (IGST). An 18% sale inside Maharashtra is therefore 9% CGST + 9% SGST; the same sale to Karnataka is 18% IGST.
Worked example
A shop in Kolkata sells a mixer grinder for ₹10,000 before tax to a customer in Kolkata. The GST rate is 18%.
- GST = 10,000 × 18 ÷ 100 = ₹1,800, split as CGST ₹900 + SGST ₹900.
- Total = 10,000 + 1,800 = ₹11,800.
Now the reverse: the shelf price is ₹11,800 including GST. Taxable value = 11,800 × 100 ÷ 118 = ₹10,000 and GST = ₹1,800. A common mistake is to take 18% of ₹11,800 (₹2,124), which overstates the tax. The GST share of an inclusive price at 18% is 18/118, about 15.25%.
GST rates after GST 2.0 (from 22 September 2025)
On the recommendation of the 56th GST Council meeting on 3 September 2025, most goods moved to two main rates, 5% and 18%, with 40% for a short list of luxury and “sin” goods. The new goods rates were notified in Notification No. 9/2025-Central Tax (Rate) dated 17 September 2025 and apply from 22 September 2025. Pan masala and tobacco products moved to 40% from 1 February 2026 (Notification No. 19/2025-Central Tax (Rate) dated 31 December 2025), when the compensation cess on them ended.
| Total GST | Examples (always check your exact HSN code) |
|---|---|
| 0% (nil / exempt) | Fresh milk, UHT milk, paneer, bread, roti and paratha, printed books, exercise books, individual life and health insurance |
| 5% | Butter, ghee, namkeen, biscuits, most medicines, hair oil, toothpaste, toilet soap bars, many daily-use items |
| 18% | Most other goods and services: cement, ACs, TVs, small cars, IT, consulting and repair services |
| 40% | Pan masala, cigarettes and tobacco, sugary aerated drinks, larger cars and SUVs |
| 3%, 1.5%, 0.25% | Gold, silver and jewellery (3%); cut and polished diamonds (1.5%); rough diamonds (0.25%) |
Rates depend on the exact tariff line, and sometimes on price, packing or use. Look up a code with our HSN code finder, then confirm it on CBIC.
Common mistakes
- Using old rates. 12% and 28% were removed for almost all goods on 22 September 2025. An invoice dated after that must use the new rate for the item. The calculator keeps 12% and 28% only for checking older invoices.
- Charging CGST + SGST on an inter-state sale (or IGST within the state). The place of supply decides this, not where the buyer’s head office is. If you charge the wrong type, you pay the right tax again and claim a refund of the wrong one.
- Taking the rate on an inclusive price. Divide by (100 + rate), don’t multiply.
- Rounding each tax separately on every line and getting a total that is a paisa off. Invoiqo and this calculator split the tax on the line and keep CGST + SGST equal to the total tax.
- Composition dealers adding GST. A composition taxpayer cannot collect tax from customers and issues a bill of supply instead of a tax invoice.
Official sources
- PIB: recommendations of the 56th GST Council meeting (3 Sep 2025)
- CBIC: GST rates for goods and services and CBIC tax information portal (CGST Act, Rules and notifications): Notifications 9/2025 and 10/2025-Central Tax (Rate) dated 17 Sep 2025; 19/2025-Central Tax (Rate) dated 31 Dec 2025.
Checked on 28 October 2026. Rates can change by notification; when in doubt, ask your tax adviser.