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How to calculate GST inclusive and exclusive, and take GST out of a price

Updated on 24 October 2026

The short answer. To add GST to a price, multiply by (100 + rate) ÷ 100: ₹1,000 at 18% becomes ₹1,180. To take GST out of a price that already includes it, divide by (100 + rate) ÷ 100: ₹1,180 ÷ 1.18 = ₹1,000, so the GST is ₹180. Never subtract 18% of the total, which gives ₹212.40, the wrong answer.

"GST exclusive" means the price before tax, also called the taxable value. "GST inclusive" means the price with tax already in it, which is what a shop shelf or a restaurant menu usually shows. Moving between the two is one multiplication or one division, and the only common mistake is doing the division as a subtraction.

The two formulas

You have You want Formula Example at 18%
price before GST GST amount price × rate ÷ 100 1,000 × 18 ÷ 100 = 180
price before GST price with GST price × (100 + rate) ÷ 100 1,000 × 1.18 = 1,180
price with GST price before GST price × 100 ÷ (100 + rate) 1,180 × 100 ÷ 118 = 1,000
price with GST GST amount price × rate ÷ (100 + rate) 1,180 × 18 ÷ 118 = 180

The last row is the formula in rule 35 of the CGST Rules, 2017, which says that where the value of a supply includes tax, the tax is the inclusive value times the rate, divided by 100 plus the rate.

How to take GST out of a price

  1. Find the rate that applies to the item. Since 22 September 2025 most goods and services are at 5% or 18%, with 40% for a short list of luxury and "sin" goods. The invoice or the CBIC rate schedule is the authority.
  2. Divide the inclusive price by (100 + rate) and multiply by 100. That is the taxable value.
  3. Subtract the taxable value from the inclusive price. That is the GST.
  4. For a sale within one state, split the GST in half: half is CGST, half is SGST (or UTGST in a union territory). For a sale to another state, the whole amount is IGST.
  5. Or enter the price and rate in the Reverse GST Calculator, which shows all three figures and the split for every line of a bill.

Worked examples at the current main rates

Inclusive price Rate Taxable value GST CGST + SGST
₹1,050 5% ₹1,000.00 ₹50.00 ₹25.00 + ₹25.00
₹1,180 18% ₹1,000.00 ₹180.00 ₹90.00 + ₹90.00
₹999 18% ₹846.62 ₹152.38 ₹76.19 + ₹76.19
₹1,400 40% ₹1,000.00 ₹400.00 ₹200.00 + ₹200.00

The ₹999 row shows rounding. CGST and SGST are each 9%, so each is ₹999 × 9 ÷ 118 = ₹76.1949, which rounds to ₹76.19; the two add to ₹152.38 and the taxable value is ₹999 − ₹152.38 = ₹846.62. Sold to another state, the IGST is ₹999 × 18 ÷ 118 = ₹152.3898, which rounds to ₹152.39 on a taxable value of ₹846.61. The paisa between the two is normal. Invoicing software usually rounds each tax to the paisa per line, and the bill total to the rupee.

Why subtracting 18% is wrong

18% of ₹1,180 is ₹212.40, and ₹1,180 − ₹212.40 = ₹967.60. Add 18% back to ₹967.60 and you get ₹1,141.77, not ₹1,180. The error comes from taking the percentage of the wrong base: GST is 18% of the taxable value, not 18% of the total. The tax share of an inclusive price is always smaller than the rate:

Rate Share of the inclusive price that is GST
5% 5 ÷ 105 = 4.76%
18% 18 ÷ 118 = 15.25%
40% 40 ÷ 140 = 28.57%

The rates since September 2025

The GST Council's 56th meeting on 3 September 2025 replaced the four main slabs of 5%, 12%, 18% and 28% with two, 5% and 18%, and a special rate of 40% for items such as pan masala, tobacco products, luxury cars and online gaming. The new rates took effect on 22 September 2025 for services and most goods; pan masala, gutkha, cigarettes, chewing tobacco and bidi stayed on their old 28% rate and compensation cess until the cess loans were repaid. CBIC Notification 19/2025-Central Tax (Rate) then moved pan masala and tobacco to 40%, and biris to 18%, from 1 February 2026, and omitted the 28% schedule, so no goods are at 28% now. Many items moved: a large group of packaged foods went from 12% or 18% to 5%, small cars and air conditioners from 28% to 18%, and some items to nil. A few special rates remain, such as 3% on gold and 0.25% on rough diamonds.

An old invoice may still show 12% or 28%. That is correct for its date; what matters is the rate on the day of supply.

A late GSTR-3B: the late fee and the interest, worked

Filing late costs two separate amounts. The late fee is ₹25 a day under the CGST Act and ₹25 under the State Act, or ₹10 each when the central tax payable in the return is nil, up to a cap set by last year's turnover. The interest is 18% a year on the tax paid late from the electronic cash ledger, counted from the day after the due date.

Step Figure
GSTR-3B for August 2026, due 20 September 2026
Filed 20 October 2026, 30 days late
Late fee, CGST: ₹25 × 30 days (cap ₹1,000 up to ₹1.5 crore turnover) ₹750
Late fee, SGST: the same again ₹750
Interest: ₹1,00,000 paid in cash × 18% × 30 ÷ 365 ₹1,479
Total ₹2,979

The GST late fee and interest calculator gives the same ₹2,979. The fee stops growing on day 40, at ₹1,000 under each Act (₹2,000 in all); a nil return reaches its cap of ₹250 each (₹500 in all) on day 25. Cash already in the ledger on the due date, and left there until it is debited, bears no interest.

If it doesn't work

  • Your total is off by a paisa or a rupee. Rounding: each line's tax is rounded to the paisa, and the invoice total is often rounded to the rupee. A difference that small is normal.
  • The tax you worked out is too high. You subtracted the rate from the inclusive price. Divide instead.
  • The bill shows IGST, not CGST and SGST. The seller is in another state, or it is an online order shipped across states. IGST is the whole GST at the full rate.
  • The rate you expected is not on the bill. The item may be in a different slab after September 2025, or a cess may apply as well. Check the CBIC rate schedule for its HSN or SAC code.
  • A restaurant bill shows 5% with no input tax credit. Most restaurant services are at 5% without input tax credit; the formula is the same.

Questions people ask

How do I calculate GST from an inclusive amount?

Divide the inclusive amount by 100 plus the rate, then multiply by the rate. At 18%, ₹1,180 × 18 ÷ 118 = ₹180 of GST, and the price before tax is ₹1,000. Equivalently, divide the inclusive amount by 1.18 to get the taxable value and subtract it from the total.

What is the reverse GST formula?

Taxable value = inclusive price × 100 ÷ (100 + rate), and GST = inclusive price − taxable value. Rule 35 of the CGST Rules, 2017 states it as tax = inclusive value × rate ÷ (100 + rate). At 5%, ₹1,050 contains ₹50 of tax; at 40%, ₹1,400 contains ₹400.

How do I add 18% GST to a price?

Multiply the price by 1.18. A ₹2,500 item costs ₹2,950 with 18% GST, of which ₹450 is tax. Within one state the ₹450 is shown as ₹225 CGST and ₹225 SGST; for a buyer in another state it is ₹450 IGST. At 5%, multiply by 1.05 instead.

Is 12% GST still there?

Not for goods. The rate notification in force from 22 September 2025, CBIC 9/2025, has no 12% schedule, so every good that was at 12% moved, mostly to 5% or 18%. Invoices dated before that day correctly show 12%. Services have their own notification, and a few older entries may remain, so check any specific service.

How is GST split between CGST and SGST?

Equally, for a sale within one state or union territory: an 18% GST is 9% CGST and 9% SGST, or UTGST in a union territory. For a sale between states, the whole 18% is charged as IGST, which the centre collects and shares with the destination state. The total tax is the same either way.

Sources

Checked 5 Oct 2026:

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