How to Calculate GST in India: Formulas and Examples
Learn how to add GST to a price and remove it from a GST-inclusive total, with worked examples, the CGST, SGST and IGST split and the mistakes to avoid.
By FreeToolsHub Editorial TeamPublishedUpdated 5 min read
Goods and Services Tax (GST) is the indirect tax charged on most goods and services in India. Whether you run a shop, send invoices as a freelancer or just want to check a bill, you will need to do two calculations: add GST to a price, and work out how much GST is hidden inside a price that already includes it. This guide shows both, with examples you can follow.
This article explains arithmetic. It is general information, not tax advice. Rates and rules change, so always confirm the correct rate for your goods or services with the official GST portal or a qualified tax professional.
The basics
GST is charged as a percentage of the value of the supply. The percentage depends on how the goods or services are classified, using an HSN code for goods and a SAC code for services. Because the GST Council revises rates from time to time, you should never rely on an old rate. As checked against official sources on 11 November 2026, India's two main GST rates are 5 percent and 18 percent, with a special 40 percent rate for selected goods and services, and most of the September 2025 reforms took effect on 22 September 2025. Some goods still carry lower rates such as 0.25, 1.5 and 3 percent, and 12 percent can still apply in specific cases. The official sources are the CBIC GST rates page, the CBIC notifications portal and the HSN/SAC lookup on the GST portal.
Adding GST to a price (GST-exclusive)
When a price is before GST, the tax is added on top.
- GST amount = price × rate ÷ 100
- Total = price + GST amount
Example: A service costs ₹2,500 before GST and the rate is 18 percent.
- GST = 2,500 × 18 ÷ 100 = ₹450
- Total = 2,500 + 450 = ₹2,950
Removing GST from a price (GST-inclusive)
When a price already includes GST, you work backwards.
- Price before GST = total × 100 ÷ (100 + rate)
- GST amount = total − price before GST
Example: A bill totals ₹1,180 and includes 18 percent GST.
- Price before GST = 1,180 × 100 ÷ 118 = ₹1,000
- GST = 1,180 − 1,000 = ₹180
The most common mistake
Many people try to remove GST by taking 18 percent off the total. That is wrong, because the 18 percent was calculated on the smaller, pre-tax price. For ₹1,180, 18 percent of the total is ₹212.40, which would leave ₹967.60 instead of the correct ₹1,000.
Worked examples at different rates
Here is the effect on a ₹1,000 pre-tax price at the calculator's quick rates, plus one fractional rate:
| Rate | GST on ₹1,000 | Total |
|---|---|---|
| 0% | ₹0 | ₹1,000 |
| 5% | ₹50 | ₹1,050 |
| 18% | ₹180 | ₹1,180 |
| 40% | ₹400 | ₹1,400 |
| 0.25% | ₹2.50 | ₹1,002.50 |
Use the GST Calculator to try any amount. It offers the quick rates 0, 5, 18 and 40 percent and a Custom field for anything else, such as 12 percent where it applies to a particular supply. You choose the rate; the calculator does the arithmetic.
CGST, SGST and IGST
GST is split into components depending on where the supply happens:
- Within one state: the tax is divided equally between the Centre (CGST) and the State or Union Territory (SGST or UTGST). At 18 percent that is 9 percent CGST plus 9 percent SGST.
- Between states: the full rate is charged as IGST, so 18 percent is shown as 18 percent IGST.
On a ₹1,000 pre-tax price at 18 percent, an intra-state invoice shows ₹90 CGST and ₹90 SGST, while an inter-state invoice shows ₹180 IGST. The total tax is the same either way.
Rounding
GST amounts are normally rounded to the nearest paisa. If a total involves an odd paisa, the split between CGST and SGST may differ by a paisa. When you add up many invoice lines, accounting software may round slightly differently from a single calculation, so small differences of a paisa or two are normal. Our calculator rounds once, at the end, and splits any odd paisa so the two halves always add up to the full GST.
Tips for invoices and pricing
- Check the HSN or SAC code and the current rate before issuing an invoice.
- State clearly whether a quoted price is inclusive or exclusive of GST, to avoid disputes.
- Keep the pre-tax price, the tax amount and the total as separate lines.
- If you set prices that include GST, calculate your real profit on the pre-tax amount, because the tax you collect is not your income. The profit margin guide shows how.
- For anything involving registration, returns, input tax credit or exemptions, speak to a qualified professional.
Related tools
- GST Calculator for adding and removing GST with the CGST, SGST and IGST split.
- Percentage Calculator for general percentage questions.
- Profit Margin Calculator to check your margin once you know your pre-tax price.
