Monday, November 07, 2016

Australian GST Calculator illustrates the importance of correct rounding in systems handling GST.

Over the years I've noticed in systems handling GST, rounding can be an issue. I've created a short video which illustrates the problem of rounding.

As an example, if you take the price of $1.04, this breaks down to the GST amount of 9 cents and the amount without GST is 95 cents. However if we add GST to the price of 95 cents, we don't end up with $1.04, we end up with $1.05. The reason for this is when we calculate GST based on 95 cents, we get a GST amount of 9.5 cents. Since we can't have half cents, we need to round the cents up to 10 cents. This gives us a GST inclusive price of $1.05.

This example illustrates that not all prices directly calculate to be the same in both directions. That is, adding GST to a price and determining the GST of a GST inclusive price do not all end up with the same amounts.

Next time when you're entering a purchase into your system and the cents don't quite match up, at least now you'll know why.

To help those that need to work with GST I've created a couple of calculators to assist. The first is a calculator which enables you to determine the GST amount from a price that includes GST. This calculator is located at www.AustralianGSTCalculator.com.au. The second calculator enables you to add GST to a price which does not include GST, to give you the GST inclusive price. This calculator can be found at www.AustralianGSTCalculator.com.au/add-gst.php.

I hope you find the calculators useful.

Kelvin Eldridge
www.AustralianGSTCalculator.com.au

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