Reverse GST Calculator: Take the GST Out of a Total
To reverse GST, divide the GST-inclusive total by 11. The result is the GST; what remains is the price before GST. A $1 210 invoice therefore holds $110.00 of GST and $1 100.00 of value. The shortcut fails in one common situation that most reverse GST calculators ignore: a receipt where some items are GST-free. Supermarket dockets, pharmacy receipts and mixed supplier invoices contain items on which no GST was charged, and dividing the whole total by 11 then claims GST that was never paid. The calculator below asks for that GST-free part and takes it out before dividing, so the credit you record matches the docket. It runs on the same engine as our main GST calculator, with the Act's rounding to the nearest cent.
Reverse GST from a receipt total
GST in the total
$22.18
Dividing the whole receipt by 11 would claim $26.04, overstating the credit by $3.86.
Several items on one invoice? Use the full GST calculator.
Publisher of calculators and practical guides · Finance Enthusiast
What the calculator does with your receipt
It removes the GST-free part, divides what is left by 11, rounds the GST to the nearest cent with half a cent going up, and gives you the amount before GST. With the default figures, a $286.40 docket containing $42.40 of fresh produce holds $22.18 of GST. Dividing the whole docket would have given $26.04: a credit overstated by $3.86 on a single shop, which adds up quickly over a quarter of receipts.
The data it uses is the law, not an estimate: the 10% rate of section 9-70 of the GST Act and the ten-elevenths value of section 9-75. Nothing is sent anywhere; the result updates as you type.
Reverse GST on common totals
| Total inc GST | GST (÷ 11) | Before GST | 10% of the total (wrong) |
|---|---|---|---|
| $33.00 | $3.00 | $30.00 | $3.30 |
| $165.00 | $15.00 | $150.00 | $16.50 |
| $1 210.00 | $110.00 | $1 100.00 | $121.00 |
| $4 400.00 | $400.00 | $4 000.00 | $440.00 |
| $13 200.00 | $1 200.00 | $12 000.00 | $1 320.00 |
When you need the other direction
A supplier quote written ex GST needs the opposite operation: multiply by 1.1. If you are checking a quote against the invoice that followed it, run the quote through the inclusive and exclusive converter, then compare the GST lines: they should match to the cent, or differ by one cent at most when the supplier rounds line by line.
What this tool does not do
It assumes every non-GST-free item carried the standard 10%. It does not handle input-taxed items such as bank fees or residential rent on a mixed statement (enter them as GST-free: the effect on the GST is the same, none), margin scheme property sales, or purchases you will use partly in private. For a whole invoice with many lines, the GST calculator takes each item separately; for your quarter, the BAS and GST credits simulator applies the business-use share.
Sources
Frequently Asked Questions
What is the reverse GST formula?
Why can I not just take 10% off the total?
How do I reverse GST on a receipt that mixes GST-free items?
Is reverse GST the same as a reverse charge?
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