How do you use the GST calculator?
The GST calculator estimates the Goods and Services Tax (GST) included in or added to an amount. If you have an invoice, quotation, purchase order, or billing screen in front of you, first check whether the displayed amount includes GST.
Enter that amount, select the applicable GST rate, and choose whether the amount is exclusive or inclusive of GST. You must also identify whether the supply is intra-state or inter-state before using the result on an invoice or in your records.
Amount: ₹________
GST rate: ___%
Price type: Exclusive / Inclusive
Supply type: Intra-state / Inter-state
Calculate GST
The result should show:
- Base taxable value
- GST amount
- Final total including GST
- Central Goods and Services Tax (CGST) and State Goods and Services Tax (SGST) for an intra-state supply
- Integrated Goods and Services Tax (IGST) for an inter-state supply
Choose the rate applicable to the goods or service. Do not infer the rate from the invoice total.
Check the classification and current rate through the official GST portal before issuing an invoice or claiming Input Tax Credit (ITC). The next section explains each result.
What does the GST result mean?
The result separates the taxable value from the GST charged on it. An exclusive amount is the value before GST, so the calculator adds the tax.
An inclusive amount already contains GST, so the calculator works backwards to identify the taxable value and the GST portion.
For an intra-state transaction, GST is generally divided between CGST and SGST when the applicable place-of-supply rules require that treatment. If the total GST is ₹180, the displayed split would ordinarily be ₹90 as CGST and ₹90 as SGST.
For an inter-state transaction, the ₹180 would generally be shown as IGST instead.
The result is an estimate, not a filing determination. Place of supply, exemptions, composition rules, reverse charge, cess, discounts, rounding, and classification can change the invoice treatment.
A displayed Maximum Retail Price (MRP) may already include applicable tax, so confirm whether the amount you entered is inclusive of GST. These assumptions lead directly to the methodology.
How is GST calculated?
GST is calculated by applying the selected rate to the taxable value or by extracting the tax from an inclusive total. The calculator uses the following formulas and rounds displayed rupee values to two decimal places.
For a GST-exclusive price:
GST amount = Base amount × GST rate ÷ 100
Final amount = Base amount + GST amount
For a GST-inclusive price:
Base amount = Inclusive amount × 100 ÷ (100 + GST rate)
GST portion = Inclusive amount − Base amount
For an intra-state supply where the tax is divided equally:
CGST = Total GST ÷ 2
SGST = Total GST ÷ 2
For an inter-state supply:
IGST = Total GST
The tool does not identify the correct Harmonised System of Nomenclature (HSN) classification, place of supply, or GST rate for you. Use the official GST portal to verify these inputs.
This methodology was reviewed on 11 August 2026. Rates and tax treatment can change, so check the selected rate against a dated official notification or the official GST portal before using the estimate in your records.
The worked example makes the calculation auditable.
What is a worked GST calculation?
A worked GST calculation shows each step from the entered value to the final amount. Example: Assume that a business quotes an exclusive taxable value of ₹10,000 for services and selects an illustrative GST rate of 18%.
GST = ₹10,000 × 18 ÷ 100 = ₹1,800
Final total = ₹10,000 + ₹1,800 = ₹11,800
If the supply is intra-state, the ₹1,800 GST amount is displayed as:
CGST = ₹900
SGST = ₹900
CGST and SGST together remain ₹1,800. If the same supply is inter-state, the calculator displays IGST of ₹1,800 instead.
For contrast, enter ₹11,800 as an inclusive amount at the same illustrative rate:
Base amount = ₹11,800 × 100 ÷ 118 = ₹10,000
GST = ₹11,800 − ₹10,000 = ₹1,800
The inclusive calculation reaches the same taxable value, GST amount, and final total because only the direction of the calculation changes.
Remember that an inclusive amount already contains GST, while an exclusive amount does not.
Verify the GST rate and supply type before copying the result to an invoice, return, or accounting record. The following questions cover accuracy, privacy, and next actions.
Frequently asked questions about the GST calculator
These answers address common questions about estimates, assumptions, and verification.
Is the GST calculator accurate?
The calculation is mathematically accurate when the entered amount, price type, and rate are correct. Its output can differ from an invoice when line-level rounding, discounts, cess, exemptions, or supply classification affect the calculation.
How do I know which GST rate to select?
Identify the goods or services and verify their current GST classification. Use the relevant HSN or service classification, then check official notifications or the official GST portal.
Do not rely only on a supplier’s previous invoice because the classification or applicable rate could differ.
Should I choose CGST and SGST or IGST?
Choose CGST and SGST when the applicable place-of-supply rules treat the transaction as intra-state. Choose IGST when those rules treat it as inter-state.
The supplier’s or recipient’s registration location alone does not determine the treatment for every type of supply.
Does the calculator store my amount?
Do not assume that the calculator stores or transmits your inputs unless the page’s published privacy notice confirms that it does. Enter only the amount required for the calculation.
Avoid entering invoice numbers, GST identification details, or personal information.
Can I use the result in a GST return?
Use the result as a checking estimate, not as a return determination. Reconcile it with the tax invoice, accounting records, and applicable ITC conditions.
Then verify the filing figures through the official GST portal or with a qualified tax professional.