Reverse GST Calculator: Remove or Add GST at Any Rate

Split a tax-inclusive total into the net price and the GST it contains, or add GST to a pre-tax amount, at any rate you enter.

Runs in your browserFree, no sign-upLast reviewed October 8, 2026

Breakdown

Net amount: 1,000.00; excluding tax
Tax @ 18%: 180.00
Gross amount: 1,180.00; including tax

Quick answers

How do I take GST out of a total?: Divide the GST-inclusive total by 1 plus the rate as a decimal to get the price before GST, then subtract that from the total to get the GST. At 10%, 110 ÷ 1.1 = 100, so the GST is 10. At 15%, 1,150 ÷ 1.15 = 1,000 and the GST is 150.
How much GST is in 450 including GST?: At 10% (Australia), 450 contains 40.91 GST and the price before GST is 409.09. At 15% (New Zealand) it is 58.70 GST on 391.30. At 18% (India) it is 68.64 GST on 381.36.
Why can I not just subtract the GST percentage from the total?: Because the percentage applies to the price before tax, not to the total. Taking 10% off 110 gives 99, but the real pre-GST price is 100. Taking 18% off 1,180 gives 967.60 instead of 1,000. Always divide rather than subtract.
How do I work out the GST component in Australia?: Divide the GST-inclusive price by 11. GST is 10% of the net price, which makes it one eleventh of the total. On 500 including GST, the GST is 45.45 and the GST-exclusive price is 454.55.
How do I add GST to a price?: Multiply the net price by 1 plus the rate. At 10%, 80 × 1.1 = 88. At 15%, 750 × 1.15 = 862.50. At 18%, 1,000 × 1.18 = 1,180. Choose the Before tax option to have the calculator do it.
How do I remove 18% GST from an amount?: Divide by 1.18. An inclusive amount of 1,000 is 847.46 before GST with 152.54 of tax. An amount of 5,900 is 5,000.00 before GST with 900.00 of tax, which splits into 450.00 CGST and 450.00 SGST.

About GST / VAT Calculator

To take GST out of a total, divide by 1 plus the rate: at 10% divide by 1.1, at 15% by 1.15, at 18% by 1.18. This calculator does that for any rate. Enter the amount, enter the tax rate, choose the After tax option and it shows the net amount, the tax and the gross amount. A total of 1,180 at 18% is 1,000.00 net plus 180.00 GST. The Before tax option works the other way and adds the tax on top. Because you type the rate yourself, it also handles VAT and sales tax, and a tick box splits the tax into equal CGST and SGST halves for Indian intra-state invoices.

GST fraction and divisor for each rate

To remove tax, divide the inclusive total by the divisor. To find just the tax, multiply the total by the fraction. The Tax inside 100 and Net inside 100 columns show how an inclusive total of 100 splits at each rate.

Rate	Divide total by	Tax as a fraction of the total	Tax inside 100	Net inside 100	Where the rate is used
5%	1.05	1/21	4.76	95.24	Canada (federal GST), India lower slab
9%	1.09	9/109	8.26	91.74	Singapore
10%	1.1	1/11	9.09	90.91	Australia
12.5%	1.125	1/9	11.11	88.89	New Zealand before October 2010
15%	1.15	3/23	13.04	86.96	New Zealand
18%	1.18	9/59	15.25	84.75	India standard slab
20%	1.2	1/6	16.67	83.33	UK standard VAT
40%	1.4	2/7	28.57	71.43	India rate on a short list of luxury and sin goods

Rates change and many goods are zero-rated or exempt. Confirm the rate that applies to your item with the relevant tax authority.

Formula to remove GST and to add GST

Remove GST: net = total ÷ (1 + rate ÷ 100), GST = total − net Add GST: GST = net × rate ÷ 100, total = net + GST GST straight from the total: GST = total × rate ÷ (100 + rate)

The net amount is the price before tax and the total is the price including tax. With a total of 847.50 at 15%: 847.50 ÷ 1.15 = 736.96 net, and 847.50 − 736.96 = 110.54 GST. The third formula is the shortcut behind the well-known fractions: at 10% it becomes total × 10 ÷ 110, which is total ÷ 11, and at 15% it becomes total × 3 ÷ 23.

GST-inclusive amounts split at 10%, 15% and 18%

Each cell shows the GST contained in the total, followed by the price before GST.

Total including GST	At 10%	At 15%	At 18%
50	4.55 GST, 45.45 net	6.52 GST, 43.48 net	7.63 GST, 42.37 net
110	10.00 GST, 100.00 net	14.35 GST, 95.65 net	16.78 GST, 93.22 net
200	18.18 GST, 181.82 net	26.09 GST, 173.91 net	30.51 GST, 169.49 net
450	40.91 GST, 409.09 net	58.70 GST, 391.30 net	68.64 GST, 381.36 net
500	45.45 GST, 454.55 net	65.22 GST, 434.78 net	76.27 GST, 423.73 net
1,000	90.91 GST, 909.09 net	130.43 GST, 869.57 net	152.54 GST, 847.46 net
1,150	104.55 GST, 1,045.45 net	150.00 GST, 1,000.00 net	175.42 GST, 974.58 net
2,500	227.27 GST, 2,272.73 net	326.09 GST, 2,173.91 net	381.36 GST, 2,118.64 net
5,000	454.55 GST, 4,545.45 net	652.17 GST, 4,347.83 net	762.71 GST, 4,237.29 net

Worked examples: removing GST, adding GST and the CGST/SGST split

Pulling the GST out of a New Zealand receipt

Amount 847.50, Tax rate 15, After tax — remove tax from it

Net amount 736.96, Tax @ 15% 110.54, Gross amount 847.50

Adding GST to an Australian quote

Amount 80, Tax rate 10, Before tax — add tax to it

Net amount 80.00, Tax @ 10% 8.00, Gross amount 88.00

Indian intra-state invoice from a net price

Amount 2500, Tax rate 18, Before tax — add tax to it, Show CGST / SGST split ticked

Net amount 2,500.00, Tax @ 18% 450.00, Gross amount 2,950.00. Tax split: CGST 9% 225.00, SGST 9% 225.00

Splitting an MRP at the 5% slab

Amount 1050, Tax rate 5, After tax — remove tax from it

Net amount 1,000.00, Tax @ 5% 50.00, Gross amount 1,050.00

Removing 20% VAT from a UK price

Amount 59.99, Tax rate 20, After tax — remove tax from it

Net amount 49.99, Tax @ 20% 10.00, Gross amount 59.99

Adding 9% GST in Singapore

Amount 85, Tax rate 9, Before tax — add tax to it

Net amount 85.00, Tax @ 9% 7.65, Gross amount 92.65

CGST, SGST and IGST in India

India divides GST according to where the supply takes place. When buyer and seller are in the same state, half of the tax goes to the central government as CGST and half to the state as SGST, so an 18% rate appears on the invoice as 9% plus 9%. Ticking the split option adds a small table with those two equal lines and their total. In a union territory without its own legislature, the state half is called UTGST.

When goods or services cross a state border, a single IGST at the full rate applies instead. The calculator has no separate IGST line because none is needed: the IGST amount is simply the Tax figure in the Breakdown panel.

Since 22 September 2025 the main Indian slabs are 5% and 18%, with a 40% rate on a narrow list of luxury and sin goods and 0% on essentials. The earlier 12% and 28% slabs were removed, so invoices dated before that change may still need those rates. Type whichever rate applies in the Tax rate field. Compensation cess is not calculated.

Limits worth knowing before you rely on the figures

One rate per calculation. For an invoice with items at different rates, run each rate separately and add the results.
Results are rounded to two decimal places. Accounting software often rounds each invoice line, so a multi-line invoice total can differ by a cent or a paisa.
The CGST and SGST split is always two equal halves of the tax. It does not check whether a supply is intra-state.
It does not decide whether an item is taxable, zero-rated or exempt, and it does not handle reverse charge, input tax credits or cess.
The rate field is set up for 0 to 100 in steps of 0.1, which covers rates such as 12.5%.
Amounts are plain numbers with no currency symbol, so the same figures apply in dollars, rupees or pounds.

Step by step

1
Enter the Amount: the total you paid if you are removing GST, or the pre-tax price if you are adding it.
2
Enter the Tax rate as a percentage, for example 10 for Australia, 15 for New Zealand or 18 for the standard Indian rate.
3
Under The amount above is, choose "After tax — remove tax from it" to take the tax out, or "Before tax — add tax to it" to put it on top.
4
Tick Show CGST / SGST split (India) if you need the tax divided into two equal halves.
5
Read Net amount (excluding tax), the Tax figure and Gross amount (including tax) in the Breakdown panel.

Answers to common questions

What does reverse GST mean?

It means working backwards from a price that already includes GST to the price before tax and the tax amount. It is sometimes called extracting or removing GST. It is unrelated to the reverse charge mechanism, where the buyer rather than the seller pays the tax to the government.

What is the difference between GST inclusive and GST exclusive?

A GST-inclusive price already contains the tax and is what the customer pays. A GST-exclusive price is the amount before tax. At 10%, an exclusive price of 100 is an inclusive price of 110. In the calculator these are the Gross amount and the Net amount.

Is the GST 10% of the total price in Australia?

No. It is 10% of the price before GST, which works out to one eleventh, about 9.09%, of the total. On a total of 200 the GST is 18.18, not 20.

What is the 3/23 rule for New Zealand GST?

Multiplying a GST-inclusive amount by 3 and dividing by 23 gives the GST inside it at the 15% rate, because 15 ÷ 115 simplifies to 3/23. On 1,150 that is 150 of GST. Dividing by 1.15 to get the net amount gives the same answer.

Can I use this as a VAT calculator?

Yes. The maths for VAT, GST and sales tax is identical. Enter the VAT rate, for example 20 for the UK standard rate, and choose whether the amount is before or after tax. At 20% the VAT is one sixth of the inclusive price.

How do I calculate GST on a discounted price?

Apply the discount first, then calculate GST on the reduced price. Enter the discounted net price as the Amount with the Before tax option. If the discounted price already includes GST, enter it with the After tax option to see the tax inside it.

Which figure should I record in my accounts?

If you are registered for GST, sales and expenses are normally recorded at the net amount and the tax is tracked separately, because GST you collect is passed on and GST you pay may be claimable. Check your own obligations with your accountant or tax authority.

Does the calculator know the GST rate for my country?

No. The Tax rate field opens at 18 and you change it to whatever applies. That keeps the tool usable anywhere and after any rate change, but it means the rate is your responsibility to confirm.

What happens if I enter a rate of 0?

The net and gross amounts are the same and the tax is 0.00. That is the correct result for zero-rated or GST-free items.