Find out how to calculate GST accurately with our guide. The page covers the new GST rates that were implemented following the GST 2.0 reform in 2025.
What is GST?
The Goods and Services Tax (GST) is India’s unified indirect tax on the supply of most goods and services, introduced in July 2017 to replace a patchwork of separate central and state taxes — excise duty, service tax, VAT, and others — with one tax structure applied across the country. Instead of tax being charged at every stage of production with little coordination between states, GST is a destination-based tax: it’s collected at each stage of the supply chain, but businesses can claim credit for the GST they already paid on their inputs, so the tax ultimately falls on the final consumer, not on the businesses in between.
A GST calculator does one specific job well: given an amount and a rate, it works out the tax and the total, or works backwards from a total to find the tax hidden inside it. It does not tell you which rate applies to your specific product — that depends on classification rules explained further down.
The GST 2.0 reform: what changed in September 2025
For its first eight years, GST ran on five main slabs: 0%, 5%, 12%, 18% and 28%, plus a compensation cess on top of 28% for certain luxury and sin goods. That structure was widely criticised for being complicated — businesses often disagreed with tax authorities about which of the middle slabs (12% or 18%, or 18% or 28%) a particular product belonged in.
The 56th GST Council meeting addressed this with a reform referred to as “GST 2.0,” effective from 22 September 2025. The core change was consolidation: the 12% slab was folded into 5%, and the 28% slab was folded into 18%, leaving two primary working rates instead of four. A new 40% slab was created specifically for a narrow list of luxury and “sin” goods — items like pan masala, aerated and caffeinated beverages, and high-end vehicles — replacing the old system of 28% plus a separate compensation cess with one combined headline rate.
The GST slabs as they stand under GST 2.0:
| Rate | What it generally covers |
|---|---|
| 0% (exempt) | Unbranded food grains, fresh fruit and vegetables, milk, salt, and most healthcare and education services |
| 0.25% | Rough diamonds and similar unprocessed precious stones |
| 3% | Gold, silver, platinum and articles of precious metal |
| 5% | The largest working slab post-reform — most packaged food, everyday essentials, and mass-consumption goods, plus items that moved down from the old 12% slab |
| 18% | The standard rate — most manufactured goods, electronics, professional and technical services, IT/software, and items that moved down from the old 28% slab |
| 40% | A narrow “demerit” slab for luxury and sin goods — tobacco products, aerated and caffeinated drinks, premium vehicles, and similar items |
If you’re used to the old five-slab system, the main thing to unlearn is that 12% and 28% no longer exist as standalone rates — items that used to sit there have moved to 5% or 18% respectively (with a select few luxury/sin items moving up to the new 40% slab instead).
CGST, SGST, and IGST: why GST has three names for one tax
This is one of the more confusing parts of GST for beginners, so it’s worth walking through slowly.
When a sale happens within the same state — say, a shop in Mumbai selling to a customer in Mumbai — the GST charged is split into two equal halves:
- CGST (Central GST) — collected by the central government
- SGST (State GST) — collected by the state government
So an 18% GST rate on an intra-state sale becomes 9% CGST + 9% SGST, adding up to the same 18% total. Both amounts appear separately on the invoice.
When a sale happens between two different states — a shop in Mumbai selling to a customer in Delhi — the full rate is charged as a single tax instead:
- IGST (Integrated GST) — collected by the central government, then apportioned to the destination state based on where the goods or services were actually consumed
So an 18% IGST rate on an inter-state sale is just 18% IGST — no split, no separate CGST/SGST lines.
The total tax paid by the customer is identical either way; only how it’s divided and administered between the central and state governments changes, based on where the supply is considered to take place. Getting this classification right matters for GST-registered businesses — charging CGST+SGST on what should have been an inter-state (IGST) transaction, or vice versa, is a genuine compliance error, not just a paperwork nitpick.
How to add GST to a price
If you have a base price and need to add GST, the formula is:
GST amount = base amount × (rate ÷ 100) Total (GST-inclusive) = base amount + GST amount
For example, a base price of ₹10,000 at 18% GST: GST amount = ₹10,000 × 0.18 = ₹1,800. Total = ₹10,000 + ₹1,800 = ₹11,800.
How to remove GST from a price (reverse GST calculation)
This is the calculation people get wrong most often. If you have a GST-inclusive price and want to know the base amount and the tax hidden inside it, you cannot simply multiply the total by the rate — that overstates the tax, because the rate applies to the base amount, not the total.
The correct formula is:
Base amount = total ÷ (1 + rate ÷ 100) GST amount = total − base amount
For example, a GST-inclusive total of ₹11,800 at 18% GST: base amount = ₹11,800 ÷ 1.18 = ₹10,000. GST amount = ₹11,800 − ₹10,000 = ₹1,800.
The common mistake: taking ₹11,800 × 18% = ₹2,124 and assuming that’s the GST amount. It isn’t — that calculation treats 18% of the total as the tax, when the actual tax is 18% of the base, which is a smaller number. This mistake overstates the tax by a meaningful margin and can throw off pricing, invoicing, and profit calculations if repeated across many transactions.
Who is the Composition Scheme for?
Separately from the standard GST slabs, small businesses below a certain turnover threshold can opt into the GST Composition Scheme, which lets them pay tax at a flat, lower rate on their total turnover instead of the standard slab rates, in exchange for simplified compliance and giving up the ability to claim input tax credit. This calculator is built for standard-rate GST calculations, not the Composition Scheme’s flat rates — if your business is registered under Composition, your applicable rate and rules are different from what’s shown here.
Common GST calculation mistakes
Adding GST on top of a GST-inclusive price. If a listed price already includes GST, adding tax again produces a double-taxed figure. Always check whether a quoted price is inclusive or exclusive of GST before calculating anything further.
Using the wrong rate for the reverse calculation. As covered above, working backwards from a total requires dividing by (1 + rate/100), not multiplying the total by the rate directly.
Assuming every product in a broad category shares one rate. GST rates are assigned by specific HSN (goods) or SAC (services) code, not by general category. Two products that seem similar in everyday language can sit in different slabs depending on their exact classification — this calculator applies whatever rate you tell it to, but it cannot look up the correct rate for you.
Confusing CGST/SGST with IGST for the wrong transaction type. Charging the wrong split based on an incorrect read of the place-of-supply rules is a compliance issue, not just an arithmetic one — when in doubt, this is worth confirming with a tax professional rather than guessing.
Forgetting that rates can change. GST rates are set by the GST Council and have changed materially before, including in the September 2025 reform covered above. A rate that was correct a year ago may no longer be correct today.
Frequently asked questions
What are the current GST rates in India? Following the GST 2.0 reform effective 22 September 2025, the main slabs are 0%, 5%, 18% and 40%, with a special 3% rate on gold, silver and precious-metal articles, and 0.25% on rough diamonds. The exact rate for any specific item depends on its HSN or SAC classification.
What’s the difference between CGST, SGST and IGST? CGST and SGST apply together on sales within the same state, splitting the GST rate equally between the central and state governments. IGST applies as a single combined tax on sales between two different states, collected centrally and then apportioned to the destination state.
How do I calculate GST backwards from a total price? Divide the GST-inclusive total by (1 + rate ÷ 100) to get the base amount, then subtract that base amount from the total to find the GST amount. Multiplying the total directly by the rate gives an incorrect, inflated figure.
Does this calculator tell me which GST rate applies to my product? No. GST rates are assigned by specific HSN/SAC classification and can have exceptions even within a general category. This tool calculates the tax once you already know the applicable rate — confirm the exact rate on the official GST portal or with a tax professional before invoicing.
Is GST the same as VAT or sales tax? GST is India’s version of a value-added tax. It replaced a collection of earlier separate indirect taxes (VAT, service tax, excise duty, and others) with a single unified structure applied nationwide, with credit for tax already paid at earlier stages of the supply chain.
Did the old 12% and 28% GST slabs disappear completely? Yes, as standalone slabs. Under the GST 2.0 reform, most items that were previously taxed at 12% moved to 5%, and most items previously at 28% moved to 18%. A narrow set of luxury and sin goods moved to a new 40% slab instead.
This article and the GST Calculator are for general informational purposes only and do not constitute tax advice. GST rates vary by HSN/SAC classification, can include exceptions, and are subject to change by the GST Council. Confirm the exact rate applicable to your goods or services on the official GST portal or with a qualified tax professional before relying on any calculation for invoicing or compliance purposes.