How to Add GST to an Amount in Australia

For a standard taxable sale, the first two formulas are the ones you need when adding GST.

You can also use the BizCalc GST Calculator to calculate the GST component and total price.

There are two ways to do it.

Method 1: Calculate the GST and add it

Take the GST-exclusive price and multiply it by 10%.

For a $250 price:

Then add the GST to the original price:

Method 2: Multiply by 1.10

You can reach the same answer in one calculation:

Multiplying by 1.10 works because the final amount consists of the original 100% price plus 10% GST.

If the GST-exclusive amount is in cell A2, calculate the total including GST with:

To calculate just the GST:

If A2 contains 820:
GST: $82.00
Total including GST: $902.00

These formulas are useful for straightforward individual amounts. More complex invoices with multiple taxable line items can involve specific GST rounding rules.

No.

The × 1.10 formula assumes that the amount is GST-exclusive and relates to a taxable sale.

Not every sale is taxable. Some supplies are GST-free or input taxed, and the GST treatment depends on what is being supplied and the circumstances of the transaction.

A sale is generally taxable if you are registered or required to be registered for GST, the sale is for payment, is made in the course of operating your business, is connected with Australia, and is not GST-free or input taxed.

So you should not automatically multiply every invoice subtotal by 1.10.

GST registration and the mathematical calculation are separate issues.

For most Australian businesses and enterprises, the GST registration threshold is $75,000 of GST turnover.

The ATO assesses both:

• current GST turnover — generally the current month plus the previous 11 months
• projected GST turnover — generally the current month plus the next 11 months

There are important qualifications to those tests. For example, the ATO states that a business whose current GST turnover is at or above the threshold may not have to register if its projected GST turnover is below the threshold.

Once a business is required to register, it generally has 21 days to do so. Different rules apply in certain situations. Taxi, limousine and ride-sourcing operators, for example, must generally register regardless of their GST turnover.

See the ATO's GST registration guidance.

If you should already have registered but haven't, the situation is different. The ATO says you may still have to pay GST on sales from the date you were required to register, even if you did not include GST in the prices you charged.

If that applies to you, the correct treatment will depend on your circumstances.

If you sell directly to consumers, how you display the price matters as well as how you calculate it.

The ACCC says businesses must display the minimum total price as a single figure, including taxes such as GST and unavoidable or pre-selected fees. If a partial price is also displayed, the total price must be at least as prominent.

See the ACCC's price display guidance.

The ACCC makes an important distinction for business-to-business pricing: where prices are displayed only to other businesses, GST does not have to be included in the displayed total price.

That distinction is particularly relevant to trades and service businesses that deal with both commercial customers and consumers.

Some GST calculations produce fractions of a cent.

For a tax invoice containing one taxable sale, the ATO says the GST amount should be rounded to the nearest cent, with half a cent rounded upwards.

Where an invoice contains more than one taxable sale, the ATO provides two methods known as the total invoice rule and the taxable supply rule.

This is one reason a manual calculation and accounting software can occasionally produce a small rounding difference on a multi-line invoice.

For a straightforward single taxable sale, calculate the GST and round the resulting GST amount to the nearest cent in accordance with the ATO's rounding rules.

Adding GST and deciding what your underlying selling price should be are two different calculations.

Example underlying selling price:
$400 excluding GST

GST-inclusive:

Use the Margin Calculator to check how your costs and underlying selling price affect margin.

If you are deciding whether to pass on all of the GST or keep the customer price unchanged, read Should I Absorb GST or Add It to My Prices?

Removing GST is not the reverse of adding 10%.

If a price is already GST-inclusive, don't simply subtract 10%.

Example GST-inclusive amount:
$110

Why divide by 11?

The GST-inclusive price represents 110% of the original price. GST therefore represents 10 parts of that 110-part total, which is one-eleventh.

See How to Remove GST From a Total for the reverse calculation and worked examples.

For a standard taxable sale where your starting price is excluding GST:

Example:

Before applying the formula, make sure the starting amount does not already contain GST and that GST applies to the sale.