India GST arithmetic
GST calculator: add or remove included tax
Start with a price before tax or a total that already includes GST. Enter the rate you have checked, then compare the base, tax and gross amount.
By Invoodle · Updated · Guidance reviewed October 2026
This tool calculates one assumed rate on one amount. It does not choose a rate, validate GST registration, determine place of supply or produce a complete tax invoice. Cess, mixed rates, special valuation, reverse-charge decisions and filing are outside its scope.
Starts with a fictional ₹10,000 example at 18%. Enter your checked amount and combined rate.
Use a decimal point, without commas or currency symbols. Up to 2 decimal places.
Enter your verified combined rate. The buttons below are examples, not a rate catalogue.
Choose a presentation only after checking place of supply and applicable rules. This switch does not determine the legal tax head.
Illustrative calculation
- Taxable value used
- ₹10,000.00
- Illustrative CGST @ 9%
- ₹900.00
- Illustrative SGST/UTGST @ 9%
- ₹900.00
- Total GST
- ₹1,800.00
- Gross total
- ₹11,800.00
Amounts round to paise. Each illustrative half rounds separately; any displayed adjustment reconciles those halves to total GST. It is not a tax head or a filing instruction. Check required invoice and reporting rounding.
Calculation only: no registration check, classification, cess, special valuation, reverse-charge decision or invoice export. Inputs stay in this calculator; they do not replace your saved draft.
Add GST or work backwards from an inclusive price
For a base B and combined rate r%, tax = B × r ÷ 100 and gross = B + tax. For a total T containing only that GST, base = T × 100 ÷ (100 + r), with tax = T − base. These formulas assume the entered value is the correct starting amount; the calculator does not determine statutory valuation.
At an assumed 18%, ₹11,800 ÷ 1.18 gives a ₹10,000 base. Taking 18% off the gross instead gives ₹9,676, because it applies the percentage to the wrong starting amount. Use the inclusive mode when GST is already in the price.
| Input and mode | Base | GST | Gross |
|---|---|---|---|
| ₹10,000, add GST | ₹10,000.00 | ₹1,800.00 | ₹11,800.00 |
| ₹11,800, remove included GST | ₹10,000.00 | ₹1,800.00 | ₹11,800.00 |
Read the rounding note before copying small amounts
On ₹0.03 before tax at an assumed 18%, GST rounds to ₹0.01 and gross to ₹0.04. Each equal illustrative half rounds to ₹0.01, so a −₹0.01 display adjustment reconciles the two halves with total GST. That adjustment is not another tax head. Confirm the invoice and reporting rules for your case; the display method does not implement statutory rounding of liabilities.
Check the rate and tax treatment before using the numbers
The 0%, 5% and 18% buttons are arithmetic shortcuts. They are not an exhaustive or current rate schedule. Verify classification, supply date, notification conditions and any cess or exemption separately. A Council recommendation and an effective government notification are different steps; this calculator does not maintain a legal rate database.
Ordinary domestic tax-head treatment compares supplier location with the legal place of supply, subject to the supply rules and exceptions. Special cases, including SEZ, imports/exports and reverse charge, need separate review. Choosing the illustrated split does not make that determination or establish input-tax-credit eligibility.
The invoice editor has different field limits
The editor has supplier GST-number entry and one general Tax total. Dedicated buyer GSTIN, HSN/SAC, place-of-supply, reverse-charge and separate tax-head controls are absent. Its single percentage applies to subtotal before the separate order discount. Calculator values are not transferred into a draft, and this illustration is not a complete statutory invoice.
Official references
- CBIC: CGST Rule 35 inclusive-tax formula — June 2021 compilation, read with current amendments
- CBIC: IGST Act sections 7–8 and supply rules — read with current amendments
- India Code: CGST Act, valuation, collection, invoices and rounding provisions
- CBIC: invoice particulars — read with current amendments
Older CBIC compilations provide the linked framework; check current amendments and applicable notifications for the actual supply.
GST calculator questions
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