How to calculate GST
GST is added to a net amount or extracted from a gross one. To remove GST at 5%, divide the total by 1.05, not by 0.95: $1,050 including 5% GST is $1,000 net and $50 of tax.
Remove GST: net = total ÷ (1 + rate); GST = total − net
At 10%, the GST inside a GST-inclusive price is one eleventh of it; at 15% it is three twenty-thirds. Both come from the same division, so the calculator gives the same answer either way.
Worked examples at the preset rates
The same $1,000 net amount at each preset in the calculator, and the reverse from a GST-inclusive total. Rates change and vary by what you sell, so the presets are starting points rather than advice.
| Preset | Net | GST | Total |
|---|---|---|---|
| Canada 5% | $1,000.00 | $50.00 | $1,050.00 |
| Singapore 9% | $1,000.00 | $90.00 | $1,090.00 |
| Australia 10% | $1,000.00 | $100.00 | $1,100.00 |
| New Zealand 15% | $1,000.00 | $150.00 | $1,150.00 |
| India 18% | $1,000.00 | $180.00 | $1,180.00 |
Read the table backwards to remove GST: a $1,100 total at 10% is $1,000 net and $100 of GST, which is the one eleventh.
Removing GST is not subtracting it
To take 5% GST out of a $1,050 total you divide by 1.05, which gives $1,000 net and $50 of tax. Subtracting 5% of $1,050 gives $997.50, which is wrong by $2.50 on a small number and by real money on a large one.
The higher the rate the worse it gets. On a $1,180 total at 18%, subtracting 18% leaves $967.60 instead of $1,000, a gap of $32.40.
India: CGST, SGST and IGST
An Indian GST invoice splits the tax by where the supply goes. Within one state the rate is shared equally between central and state GST, so 18% appears as 9% CGST and 9% SGST. Between states the whole rate is charged as IGST. The total is the same; only the lines on the invoice differ. Work the GST out here, then show it as two halves or one line to match the supply.
Canada: GST, HST and provincial tax
The Canada preset is the federal GST. Provinces either add their own sales tax on top or charge a single harmonized HST in its place. If your customer is in a province with HST or a provincial tax, type the combined rate into the rate field; the arithmetic is the same.
GST, VAT and sales tax
GST and VAT work the same way: charged at each stage, with businesses reclaiming what they paid, so the tax lands on the final buyer. Different countries use different names for the same mechanism.
US sales tax is different in kind. It is charged once, at the point of sale to the end customer, and businesses buying for resale are exempt rather than reclaiming. If you are selling in the United States, the sales tax calculator is the right page.
On the invoice, show three lines
Net, GST, total. A tax-inclusive single figure is the one that gets queried, because the other side needs the tax broken out to reclaim it. The button under the result carries the net amount into the invoice generator with the rate already set, so the document does the split for you. The tax invoice entry lists what else the document usually needs.
Related calculators
- VAT calculatorAdd or remove VAT for 40 countries
- Invoice calculatorLine items, discount, GST and deposit into a balance due
- Sales tax calculatorUS sales tax by state
Questions people ask
How do I remove GST from a total?
Divide the GST-inclusive total by one plus the rate. At 5%, divide by 1.05. Subtracting 5% from the total instead is a common mistake and gives a smaller, wrong answer.
How do I add GST?
Multiply the net amount by the rate and add it on, or multiply the net by one plus the rate to get the total directly.
What is the GST rate?
It depends on the country and often on what you are selling. Canada is 5% federally with provincial additions, India uses several slabs including 18%, Australia is 10%, New Zealand 15% and Singapore 9%. Rates change, so check the current one.
How do I work out the GST in a GST-inclusive price?
Divide the price by one plus the rate to get the net, then subtract the net from the price. At 10%, that is the same as dividing the price by 11; at 15%, multiplying it by 3 and dividing by 23.
How do I split 18% GST into CGST and SGST?
Halve it. Within one Indian state, 18% is charged as 9% CGST and 9% SGST. Between states the full 18% is charged as IGST instead.
Can I use this for HST or a combined provincial rate?
Yes. Type the combined rate into the rate field. Adding or removing HST is the same arithmetic as GST: multiply by one plus the rate to add it, divide by it to take it out.
Is GST the same as VAT?
Mechanically, yes: both are charged at each stage with businesses reclaiming what they paid. The name differs by country. For Europe and the UK the VAT calculator covers the same ground with the right wording.
Is GST the same as US sales tax?
No. Sales tax is charged once, to the final customer, and resellers are exempt rather than reclaiming. For the United States, use the sales tax calculator.
Should the invoice show GST separately?
Yes. The other side usually needs the tax broken out to reclaim it, and a single tax-inclusive figure is the one most likely to be queried.