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For businessesRates reviewed September 2026

GST Calculator: Inclusive and Exclusive GST

A GST calculator answers two questions that come up on every invoice: how much tax to add to a price, and how much tax is already buried inside a price. Both use the same rate, but the arithmetic runs in opposite directions, and getting the direction wrong is the most common reason a sales register and a GSTR-1 fail to tie out.

The slab structure changed materially on 22 September 2025. The GST Council, at its 56th meeting on 3 September 2025, recommended collapsing the 12 percent and 28 percent slabs into 5 percent and 18 percent, and introducing a single 40 percent rate for luxury and demerit goods. CBIC notified the change on 17 September 2025 and it took effect on 22 September 2025. Individual life and health insurance premiums became exempt on the same date.

Rate alone is not the whole answer. Whether the tax splits into CGST and SGST or is charged wholly as IGST depends on the place of supply, and whether you charge GST at all depends on registration thresholds and on whether you have opted into the composition scheme. This page covers all four.

GST Calculator

The price on the invoice, before or after GST depending on the next choice.

₹

Slabs as notified with effect from 22 September 2025.

Same state as the supplier means the rate splits in half; a different state means IGST.

Total GST

₹1,800

at 18% on a taxable value of ₹10,000

Taxable valuebacked out of the inclusive price
₹10,000
GST rate applied
18%
CGST (9%)
₹900
SGST (9%)
₹900
Total GST
₹1,800
Invoice valuetaxable value plus GST
₹11,800
Tax as a share of the invoice
15.25%
  • Intra-state supplies split the rate equally between CGST and SGST.
  • Round the tax on each invoice to the nearest rupee under section 170.

The formula

GST amount = Taxable value × GST rate ÷ 100; Taxable value = Invoice value × 100 ÷ (100 + GST rate)

Taxable value
The price of the supply before GST, also called the assessable value or the GST exclusive value.
Invoice value
The GST inclusive amount the recipient actually pays.
GST rate
The slab applicable to the HSN code for goods or the SAC code for services.

On an intra-state supply the rate splits equally into CGST and SGST; on an inter-state supply the whole rate is charged as IGST.

How to calculate it

  1. 1

    Fix the taxable value

    Start from the transaction value under section 15: the price actually paid or payable, including packing, commission and any incidental charges billed to the recipient. Discounts shown on the face of the invoice come out; post-supply discounts only come out if they were agreed before the supply and can be linked to the invoice.

  2. 2

    Identify the correct slab

    Match the HSN or SAC code to the rate notified with effect from 22 September 2025. The working rates are nil, 5 percent, 18 percent and 40 percent. If you are relying on a pre-September-2025 rate master, most 12 percent items have moved to 5 percent and most 28 percent items to 18 percent, so the master needs rebuilding rather than patching.

  3. 3

    Add GST, or strip it out

    If your quoted price is exclusive, multiply the taxable value by the rate. If your quoted price is inclusive, divide by 100 plus the rate and multiply by 100 to recover the taxable value, then take the difference. For 18 percent that is invoice value × 100 ÷ 118.

  4. 4

    Split the tax by place of supply

    Compare the supplier's location with the place of supply determined under sections 10 to 13 of the IGST Act. Same state means CGST plus SGST at half the rate each. Different states, or a supply to or from a union territory or a zero-rated supply, means IGST at the full rate.

  5. 5

    Check whether GST applies at all

    Below the registration threshold, and outside compulsory registration cases such as inter-state supply of goods or liability under reverse charge, you do not charge GST. A composition dealer charges nothing to the customer either and instead pays a flat percentage of turnover out of its own margin.

  6. 6

    Round and report

    Round the tax on each invoice to the nearest rupee under section 170. Report the taxable value and each tax head separately in GSTR-1, and make sure the totals agree with the outward supply figures in Table 3.1 of GSTR-3B before you file.

GST slabs effective 22 September 2025

GST slabs effective 22 September 2025
RateTypical goods and services
NilFresh milk, paneer and chena, most unprocessed food, and individual life and health insurance premiums
5%Packaged food and namkeens, soaps, shampoo and toothpaste, footwear, medicines, medical devices, agricultural machinery and most items that sat at 12 percent earlier
18%Cement, small cars and motorcycles up to 350cc, air conditioners, refrigerators, televisions, laptops, iron and steel, and professional, IT, telecom and financial services
40%Pan masala, aerated and caffeinated drinks, cars and motorcycles above the small-car thresholds, yachts, personal aircraft, and betting, gaming and casino services

Worked example

Invoice value (GST inclusive)
₹11,800
GST rate
18%
Supplier and place of supply
Both in Maharashtra
  • Taxable value = ₹11,800 × 100 ÷ 118 = ₹10,000
  • GST = ₹11,800 - ₹10,000 = ₹1,800
  • Intra-state supply, so the 18 percent splits into 9 percent CGST and 9 percent SGST
  • CGST = ₹10,000 × 9% = ₹900 and SGST = ₹10,000 × 9% = ₹900
  • If the same order were billed to a customer in Gujarat, the ₹1,800 would be charged wholly as IGST

GST = ₹1,800 (CGST ₹900 + SGST ₹900) on a taxable value of ₹10,000

Frequently asked questions

The working slabs are nil, 5 percent, 18 percent and 40 percent, effective 22 September 2025. The 12 percent and 28 percent slabs were removed at the 56th GST Council meeting held on 3 September 2025, with most 12 percent items moving to 5 percent and most 28 percent items to 18 percent. The 40 percent rate is a single demerit rate for luxury and sin goods such as pan masala, aerated drinks, large cars, yachts and casino services.
Divide the inclusive amount by 100 plus the rate, then multiply by 100. At 18 percent, an inclusive ₹11,800 gives a taxable value of ₹11,800 × 100 ÷ 118 = ₹10,000, so the GST component is ₹1,800. At 5 percent the divisor is 105 and at 40 percent it is 140.
It depends on the place of supply, not on where the goods physically move from. If the supplier's location and the place of supply are in the same state or union territory, the tax is split equally between CGST and SGST. If they are in different states, or the supply is an import or a zero-rated supply, the whole amount is IGST.
For suppliers of goods the aggregate turnover threshold is ₹40 lakh in most states and ₹20 lakh in special category states, though Jammu and Kashmir and Assam have opted for the ₹40 lakh limit. For suppliers of services it is ₹20 lakh in most states and ₹10 lakh in special category states. Registration is compulsory regardless of turnover in several cases, including inter-state supply of goods and liability to pay tax under reverse charge.
Manufacturers and traders pay 1 percent of turnover, restaurants not serving alcohol pay 5 percent, and eligible service providers under the special provision pay 6 percent. A composition dealer cannot charge GST on its invoice, cannot claim input tax credit, and files CMP-08 quarterly with an annual GSTR-4. The turnover limit is ₹1.5 crore for goods and ₹50 lakh for the service provider option.
No further slab restructuring has been notified since the rates took effect on 22 September 2025. One carve-out from that date was tobacco and pan masala containing tobacco, which continued at the earlier rate plus compensation cess during a transition tied to the settlement of the compensation cess borrowings. Check the CBIC rate notifications or the rate finder on the GST portal for the position on a specific HSN code.
GST is charged on the transaction value after any discount recorded on the face of the invoice. A post-supply discount reduces the taxable value only if it was agreed before or at the time of supply, can be linked to specific invoices, and the recipient reverses the proportionate input tax credit. Otherwise the original taxable value stands.

Sources

Rates and rules on this page come from the following. This is a working aid, not professional advice: confirm anything material with your Chartered Accountant before you act on it.

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