INTERACTIVE

GST Calculator

How to use the calculator

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Calculate GST

Note: Current GST Rate (%) in Australia is 10 %. (2021)

If input amount excludes GST

Price (ex. GST)\$1000
GST\$100
Price (inc. GST)\$1100

If input amount includes GST

Price (ex. GST)\$909.09
GST\$90.90
Price (inc. GST)\$1000

Goods & Service Tax (GST) is a tax on a business or enterprise, for the goods and services they supply/provide. A business/enterprise is liable to pay GST on a taxable turnover of \$75,000 or more (\$150,000 or more for non-profit organisations), or when providing taxi travel.

In Australia, the GST is simply calculated as a percentage/proportion (GSTRate) of the "base" price which excludes GST (PriceEx. GST):

GST=GSTRate ∙ PriceEx. GST (1)

For example, if the GSTRate = 10% = 0.10, and the PriceEx. GST = \$1000

GST=(0.10) ∙ (\$ 1000)
GST=\$ 100

The price including GST (PriceInc. GST) is then found by summing the PriceEx. GST and the GSTRate:

PriceInc. GST=PriceEx. GST+GST (2)

By substituting in Eq. 1 into Eq. 2, we can find the PriceInc. GST without needing to find the GST separately:

PriceInc. GST=PriceEx. GST+(GSTRate ∙ PriceEx. GST)

And factorising out PriceEx. GST:

PriceInc. GST=PriceEx. GST ∙ ( 1 + GSTRate) (3)

However, suppose that only the PriceInc. GST and the GSTRate are known. To find PriceEx. GST, we arrange Eq. 3:

PriceInc. GST /( 1 + GSTRate) =PriceEx. GST ∙ ( 1 + GSTRate)/( 1 + GSTRate)
PriceInc. GST /( 1 + GSTRate) = PriceEx. GST (4)

For example, if the PriceInc.GST = \$1000 and GSTRate = 10% = 0.10, the PriceEx. GST is calculated in the following way:

PriceEx. GST = PriceInc. GST /( 1 + GSTRate)
PriceEx. GST = (\$ 1000)/( 1 + 0.1)
PriceEx. GST = \$ 909.09