GST

How do you remove GST from a total amount?

The most common GST mistake in India is subtracting the rate from an inclusive figure. It gives the wrong answer every time, and always in the same direction.

Divide the inclusive total by (1 + rate÷100). For 18% GST, divide by 1.18. On an inclusive Rs 1,18,000 that gives a taxable value of Rs 1,00,000 and GST of Rs 18,000. Subtracting 18% instead would give Rs 96,760, which is Rs 3,240 too low — because the 18% was calculated on the smaller base, not on the total.

Worked out 2026-09-10 (IST) · GST-inclusive total, standard slabs

Removing GST from a Rs 1,18,000 invoice

The two methods, side by side, so the size of the error is visible.

Right and wrong, on an inclusive Rs 1,18,000 at 18 per cent
Method	Working	Taxable value	GST	Correct?
Divide by 1.18	1,18,000 ÷ 1.18	1,00,000.00	18,000.00	Yes
Multiply by 18/118	1,18,000 × 18 ÷ 118	1,00,000.00	18,000.00	Yes
Subtract 18%	1,18,000 − 21,240	96,760.00	21,240.00	No, Rs 3,240 out

Reverse GST at every slab

Taxable value and GST inside a given inclusive total
Inclusive total	At 5%	At 12%	At 18%	At 28%
500	476.19 + 23.81	446.43 + 53.57	423.73 + 76.27	390.62 + 109.38
1,000	952.38 + 47.62	892.86 + 107.14	847.46 + 152.54	781.25 + 218.75
5,000	4,761.90 + 238.10	4,464.29 + 535.71	4,237.29 + 762.71	3,906.25 + 1,093.75
10,000	9,523.81 + 476.19	8,928.57 + 1,071.43	8,474.58 + 1,525.42	7,812.50 + 2,187.50
50,000	47,619.05 + 2,380.95	44,642.86 + 5,357.14	42,372.88 + 7,627.12	39,062.50 + 10,937.50
1,00,000	95,238.10 + 4,761.90	89,285.71 + 10,714.29	84,745.76 + 15,254.24	78,125.00 + 21,875.00
1,18,000	1,12,380.95 + 5,619.05	1,05,357.14 + 12,642.86	1,00,000.00 + 18,000.00	92,187.50 + 25,812.50

The divisor to memorise. 5% → divide by 1.05. 12% → 1.12. 18% → 1.18. 28% → 1.28. To get the tax straight out, multiply the total by 5/105, 12/112, 18/118 or 28/128.

The formula

taxable value = total ÷ (1 + rate ÷ 100)

GST inside the total = total × rate ÷ (100 + rate)

the error from subtracting instead = total × rate² ÷ (100 × (100 + rate))

Check your own numbers

Switch the calculator to “remove GST” and it does the division for you at any slab.

GST CalculatorAdd or remove GST at any slab, with the CGST, SGST and IGST breakdown.

Frequently asked

Why can I not just subtract 18 per cent?

Because the 18 per cent was charged on the pre-tax value, not on the total. Take Rs 100 plus 18 per cent = Rs 118. Now subtract 18 per cent of 118, which is Rs 21.24, and you get Rs 96.76, not Rs 100. The error is rate-squared over (100 plus rate) - about 2.7 per cent of the total at the 18 per cent slab, and 6.1 per cent at 28 per cent.

What is the reverse GST formula?

Taxable value = total / (1 + rate/100), and GST = total - taxable value. Equivalently, GST = total x rate / (100 + rate). For 18 per cent that second form is total x 18/118, which is the version accountants usually memorise because it goes straight to the tax figure.

How do I find the GST inside an MRP?

An MRP on a packaged product is inclusive of all taxes by law, so use the reverse formula with the rate for that HSN code. On a Rs 500 MRP item at 18 per cent, the GST inside is 500 x 18/118 = Rs 76.27 and the pre-tax value is Rs 423.73. You cannot claim input credit from an MRP alone - you need a tax invoice showing the split.

Does the same method work for 5, 12 and 28 per cent?

Yes. Divide by 1.05, 1.12 or 1.28 respectively, or use total x rate/(100+rate) to get the tax directly: 5/105, 12/112, 28/128. The method is identical; only the divisor changes.

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