Calculate Indian GST in five steps: identify the supply and its current rate, determine the taxable value, establish the legally relevant place of supply, apply taxable value × rate ÷ 100, then show the correct components on the invoice. An ordinary intra-State supply is reported as CGST plus SGST (or UTGST in a Union Territory); an inter-State supply is generally charged as IGST. The tax acronym does not determine the rate, and the buyer’s address or a parcel’s route is not, by itself, the place-of-supply test.
The calculation in one view
For a straightforward taxable transaction, use this sequence:
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- Classify the supply and find its applicable rate. Use the current official rate entry, notification and any conditions for the particular good or service. Do not assume that every item is taxed at 18%.
- Find the taxable value. In a simple unrelated-party sale where price is the sole consideration, this is generally the transaction value. Statutory inclusions, qualifying discounts and special valuation rules can change the base.
- Determine the place of supply. Compare the supplier’s location with the legally determined place of supply under the transaction-specific rules.
- Apply the percentage. GST amount = taxable value × GST rate ÷ 100.
- Split and document it. In the ordinary intra-State case, divide the combined rate between CGST and SGST/UTGST. For an inter-State supply, apply the integrated rate as IGST and include the State name for the place of supply on the invoice.
| Transaction classification | Tax shown | Illustrative combined/rate treatment |
|---|---|---|
| Intra-State supply in a State | CGST + SGST | An 18% total example is 9% CGST + 9% SGST |
| Intra-Union-Territory supply where UTGST applies | CGST + UTGST | An 18% total example is 9% CGST + 9% UTGST |
| Inter-State supply | IGST | An 18% integrated-rate example is 18% IGST |
The percentages in the table are an arithmetic illustration only. The real rate depends on the product or service, classification, exemption status, conditions and transaction date.
How to calculate GST from taxable value
Use the basic formula
Once the taxable value and applicable rate are known:
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GST amount = taxable value × rate ÷ 100
For example, if the established taxable value is ₹10,000 and the applicable total rate is 18%:
₹10,000 × 18 ÷ 100 = ₹1,800 GST.
If the quoted amount is GST-exclusive, the invoice total before other charges is ₹11,800. This calculation does not establish that a real transaction is taxable or that 18% is the correct rate; those questions must be settled first.
When the displayed price already includes GST
If a price is GST-inclusive, do not multiply the full amount by the rate. Extract the tax instead:
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Taxable value = inclusive price − GST included
At an illustrative 18% rate, a GST-inclusive price of ₹11,800 contains ₹1,800 GST and ₹10,000 taxable value. Confirm that the stated price is actually tax-inclusive and that the same rate applies before using this reverse calculation.
How to split GST into CGST and SGST or UTGST
Ordinary intra-State split
For an ordinary intra-State supply, the combined GST rate is generally divided equally between the central and State taxes. With an 18% total rate, each component is 9%:
- Taxable value: ₹10,000
- CGST: ₹10,000 × 9% = ₹900
- SGST (or UTGST where applicable): ₹10,000 × 9% = ₹900
- Total GST: ₹1,800
- Invoice total before other charges: ₹11,800
The equal split is the ordinary structure for a combined rate. It is not a substitute for checking the rate entry: a rate table can specify the component rates directly, and special schemes or entries may require different treatment.
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Union Territory supplies
Where the law applies UTGST rather than SGST, show CGST and UTGST as separate components. The arithmetic relationship in the 18% illustration remains 9% plus 9%, but the applicable territory and statutory conditions must be verified for the transaction.
Do not split IGST into two invoice taxes
For an inter-State supply, charge the applicable integrated rate as one IGST amount. An 18% example on ₹10,000 is ₹1,800 IGST, not two separately shown 9% taxes. IGST is generally structured as the sum of the corresponding CGST and SGST/UTGST rates, but the invoice presentation is an integrated-tax line.
How to decide between CGST plus SGST/UTGST and IGST
Start with the legal place-of-supply test
The general test compares the supplier’s location with the place of supply determined under the Integrated Goods and Services Tax Act. If both are in the same State or Union Territory, the supply is generally intra-State. If they are in different States, different Union Territories, or a State and a Union Territory, it is generally inter-State.
That short rule is only the starting point. Place-of-supply provisions differ for goods and services and can contain transaction-specific rules. The legal result is not determined merely by where a courier travels, where an order was placed, or which address appears on a billing record.
Cases requiring extra care
- Goods with unusual delivery arrangements: identify the statutory place of supply rather than relying on the shipping route.
- Services: apply the service-specific place-of-supply provision; the customer’s billing address alone may not resolve it.
- Imports: imports have special inter-State treatment and additional customs-related considerations.
- Exports: export status and zero-rating questions require the applicable statutory conditions, not just a foreign address.
- Special Economic Zones: supplies to or by SEZ units or developers are among the statutory exceptions that need their own rules.
- Related or distinct persons: ordinary transaction-value assumptions may not work, so valuation rules can affect the amount.
For a complex service, export or import, SEZ transaction, or unusual movement of goods, check the specific IGST Act rule and current notification or obtain professional advice before selecting the tax type.
How to determine the taxable value
Simple transaction-value case
For unrelated parties where price is the sole consideration, the CGST Act generally uses transaction value as the taxable base. Begin with the agreed consideration, then test whether statutory additions or exclusions apply.
Amounts that may be included
The valuation provision identifies additions such as incidental expenses charged by the supplier and specified sums for which the supplier is liable but the recipient incurs. Freight, packing, commission or similar amounts cannot be excluded simply because they appear on a separate line; their treatment depends on the statutory facts.
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Discounts are conditional
A discount is not automatically removed from taxable value. Qualifying discounts can be excluded only when the statutory conditions are met. Check whether the discount was established at or before the supply, is linked to the relevant invoices where required, and whether the recipient’s input-tax-credit treatment creates an additional condition.
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When a different valuation method applies
The valuation rules provide alternatives where ordinary transaction value does not settle the amount. They cover circumstances including related or distinct persons and supplies through an agent, and can use cost-based or residual methods. In those cases, the sticker price or amount collected is not necessarily the taxable value.
Find the correct GST rate before doing the arithmetic
Use the complete rate entry
The official Central Board of Indirect Taxes and Customs rate table presents separate columns for CGST, SGST/UTGST, IGST and, where relevant, compensation cess. It also describes the supply and lists conditions. A published goods row may, for example, show 2.5% CGST, 2.5% SGST/UTGST and 5% IGST. That row demonstrates the relationship between columns; it is not a universal rate for other goods or services.
For the transaction date, confirm:
- the exact goods or service classification;
- the applicable CGST and SGST/UTGST or IGST percentages;
- any compensation cess;
- exemption wording and eligibility conditions;
- value, quantity, customer, end-use or registration conditions; and
- the current notification in force on the date of supply.
Rates, entries and interpretations can change. A calculator cannot correct a wrong classification, and a familiar 18% example must never be treated as a default rate.
Worked calculations
Example 1: intra-State supply at an illustrative 18% rate
A supplier and the legally determined place of supply are in the same State. The transaction is taxable, the taxable value is ₹10,000, and the verified total rate is 18%.
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|---|---|---|---|
| Taxable value | — | Established taxable base | ₹10,000 |
| CGST | 9% | ₹10,000 × 9 ÷ 100 | ₹900 |
| SGST | 9% | ₹10,000 × 9 ÷ 100 | ₹900 |
| Total GST | 18% | ₹900 + ₹900 | ₹1,800 |
| Invoice total | — | ₹10,000 + ₹1,800 | ₹11,800 |
Example 2: intra-Union-Territory supply at an illustrative 18% rate
Using the same ₹10,000 taxable value and 18% verified total rate, where UTGST applies, show CGST of ₹900 and UTGST of ₹900. Total GST remains ₹1,800 and the pre-other-charge invoice total is ₹11,800.
Example 3: inter-State supply at an illustrative 18% rate
The supplier and legally determined place of supply are in different States. The taxable value is ₹10,000 and the verified integrated rate is 18%.
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- IGST: ₹10,000 × 18 ÷ 100 = ₹1,800
- Invoice total before other charges: ₹10,000 + ₹1,800 = ₹11,800
These examples assume a taxable supply, a correctly established ₹10,000 base and an applicable 18% rate. They do not decide classification, exemption, place of supply or valuation for a real invoice.
Example 4: extracting tax from an inclusive price
Suppose ₹11,800 is expressly quoted as inclusive of an 18% GST rate. GST included = ₹11,800 × 18 ÷ 118 = ₹1,800. Taxable value = ₹11,800 − ₹1,800 = ₹10,000. If the applicable rate or inclusion statement differs, recalculate with those verified values.
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Invoice details you must show
Invoice rules require the document to state the taxable value, rate of tax and amount of tax. For an inter-State supply, include the place of supply with the State name. In practice, the tax section should make the classification immediately understandable:
| Supply type | Tax lines for the example | Place-of-supply entry |
|---|---|---|
| Intra-State in a State | Taxable value ₹10,000; CGST 9% ₹900; SGST 9% ₹900 | Use the applicable invoice particulars; the inter-State place-of-supply field is not the defining line |
| Intra-UT where UTGST applies | Taxable value ₹10,000; CGST 9% ₹900; UTGST 9% ₹900 | Use the applicable invoice particulars |
| Inter-State | Taxable value ₹10,000; IGST 18% ₹1,800 | State name for place of supply is required |
Other supplier, recipient, document and supply particulars also apply under the invoice rules. The table focuses on the fields directly connected with calculating and displaying the tax.
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- Describe the supply. Record the product or service, relevant classification and whether it is taxable, exempt or otherwise covered by a special treatment.
- Check the current rate entry. Record each component rate, IGST rate, cess and conditions from the current official table or notification.
- Build the taxable value. Start with transaction value where permitted; add required incidental or other statutory amounts and remove only discounts that satisfy the legal conditions.
- Identify supplier location. Use the registration and location relevant to the supply, not an informal business description.
- Determine place of supply. Apply the goods or service rule and test for import, export, SEZ and other exceptions.
- Label intra-State or inter-State. Same State/UT is generally intra-State; different States/UTs or a State and UT are generally inter-State, subject to statutory exceptions.
- Calculate. Multiply the taxable value by the verified percentage and divide by 100.
- Split or consolidate. Show CGST plus SGST/UTGST for the ordinary intra-State case, or IGST for inter-State supply.
- Complete the invoice. Include taxable value, rate, tax amount and the inter-State place-of-supply State name, along with the other required particulars.
- Recheck rounding and records. Ensure component amounts add to the stated total and retain the classification, rate and valuation basis used.
Common mistakes and how to correct them
Assuming the rate from the acronym
CGST, SGST, UTGST and IGST describe how tax is levied and allocated; they do not tell you whether the rate is 5%, 12%, 18% or another percentage. Correct the mistake by looking up the supply’s full rate entry first.
Using the customer’s billing address as the whole test
A billing address can be relevant evidence, but it is not a universal place-of-supply rule. Apply the applicable statutory provision, especially for services, imports, exports, SEZ transactions and unusual delivery arrangements.
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Physical distance or courier routing does not replace the legal place-of-supply analysis. Establish the place of supply before selecting the tax type.
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Treating the sticker price as taxable value in every case
Transaction value is generally used for a simple unrelated-party sale where price is the sole consideration. Incidental expenses, conditional discounts, related-party transactions and special valuation rules can change the base.
Splitting IGST on the invoice
When the supply is inter-State, show the applicable integrated tax as IGST. Do not print separate CGST and SGST lines merely because the integrated percentage equals their sum.
Copying a sample rate into a different product
A rate-table row is tied to its classification and conditions. Verify the exact entry and current notification for the transaction date.
Leaving the place of supply off an inter-State invoice
Invoice rules require the place of supply with State name for inter-State supplies. Add it before issuing the document and check the remaining invoice particulars as well.
When a calculator is not enough
Simple arithmetic is reliable only after legal classification and valuation are settled. Escalate the transaction for specialist review when:
- the supply combines goods and services or has several performance elements;
- the customer, supplier or intermediary is a related or distinct person;
- the transaction involves an agent, import, export or SEZ unit/developer;
- the service’s place of supply is not obvious from the customer’s location;
- a discount, reimbursement, subsidy or incidental charge affects consideration;
- the rate table contains conditions, exemptions or compensation cess; or
- the applicable notification may have changed since an earlier invoice.
In these situations, document the rule and facts supporting the result instead of relying on a generic online GST calculator.
Quick reference formulas
| Purpose | Formula |
|---|---|
| GST on an exclusive taxable value | Taxable value × rate ÷ 100 |
| Intra-State component in the ordinary equal-split case | Taxable value × (combined rate ÷ 2) ÷ 100 |
| GST included in a tax-inclusive price | Inclusive price × rate ÷ (100 + rate) |
| Taxable value from an inclusive price | Inclusive price − GST included |
| Inter-State tax | Taxable value × verified IGST rate ÷ 100 |
Use the equal-split formula only where the applicable rate entry and law produce the ordinary CGST-plus-SGST/UTGST structure. The rate and place-of-supply classification always come first.
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