GST calculator

Removing GST is dividing, not subtracting

This is the error the tool exists for, and it is worth stating before anything about rates. A gross figure of $110 at 10% does not become $99. It becomes $100.

The 10% was calculated on the net, so it is a tenth of the smaller number and an eleventh of the bigger one. Take 10% off the gross and you have taken a tenth of the wrong figure. On $110 the mistake is a dollar, which is 0.9% of the job, and it always lands on the side that costs whoever made it.

The exact shortcut worth remembering in Australia: divide the gross by 11. That works because 1 minus 1 over 1.1 is exactly one eleventh.

The shortcut does not exist at every rate, which is worth knowing

A clean whole-number divisor only turns up when 100 plus the rate divides evenly by the rate. So:

10%  Australia            gross / 11    exact
 5%  Canada, GST only     gross / 21    exact
20%  UK VAT               gross / 6     exact
13%, 14%, 15%  HST        no whole divisor exists

An Australian tradesman can do this in the van. Somebody in Ontario cannot, and that is a real difference in how much a calculator is worth to each of them.

Australia is one number. Canada is thirteen

Australian GST is 10%, nationwide, on most goods and services, and there is nothing else to establish. Registration is required at a GST turnover of $75,000, or $150,000 for a non-profit, and taxi and ride-sourcing drivers must register from the first dollar regardless of turnover.

Canada runs three systems simultaneously:

• GST only, 5%. Alberta, the Northwest Territories, Nunavut and Yukon.
• HST, a single harmonised tax. Ontario 13%, Nova Scotia 14%, and New Brunswick, Newfoundland and Labrador and Prince Edward Island at 15%.
• GST plus a provincial tax, charged separately. British Columbia 5% plus 7% PST, Manitoba 5% plus 7% RST, Saskatchewan 5% plus 6% PST, and Quebec 5% plus 9.975% QST.

So the combined rate runs from 5% to 15%. The same $1,000 invoice is $1,050 in Alberta and $1,150 in Prince Edward Island: exactly three times the tax, decided by nothing except where the customer happens to be.

And it is the customer, not you

The CRA calls this the place of supply: the rate of tax to charge depends on where you make your sale, lease or other supply. A business in Alberta selling to a customer in Ontario charges Ontario's 13%, not Alberta's 5%.

This is the most expensive thing on the page to get backwards, because it is not a one-off error. It is wrong on every invoice you issue, and it compounds quietly until somebody reconciles a return.

Two Canadian rules that get guessed wrong

PST does not sit on top of the GST

In a GST plus PST province, the obvious guess is that the provincial tax applies to the GST-inclusive figure, the way a tax on a tax normally would. It does not. The CRA is explicit: if provincial sales tax is charged in the place of supply, calculate the GST on the price without the PST.

Both are charged on the net. On a $1,000 net invoice in British Columbia that is $50 of GST and $70 of PST, a flat 12% and no more. Compounding them would produce 12.35% and add $3.50 your customer does not owe. In Quebec, where the QST is 9.975%, the same mistake adds nearly $5 and is harder to spot because the rate is already an awkward number.

HST goes on the invoice as one rate

The CRA requires the total HST rate on the paperwork and says not to show the federal and provincial parts separately. So an Ontario invoice reads 13% on one line, never 5% plus 8%, even though that is exactly what it is underneath.

In a GST plus PST province the opposite holds, and for a good reason: those genuinely are two different taxes going to two different administrations. Quebec's QST is collected by Revenu Québec rather than the CRA, which means a separate registration and a separate return alongside the federal one.

Nova Scotia is 14%, not 15%

The CRA table now reads 14% for Nova Scotia, reduced from 15%, and the CRA publishes transitional rules for the change. A great deal of writing still says 15%. If you have supplies straddling the change date, the transitional rules are the thing to read rather than the rate table.

This is also the row most likely to have moved again by the time you read this, which is why the page carries the date it was checked rather than presenting the figures as permanent.

Why there is no American version of this page

The United States has no federal consumption tax at all. What it has instead is state sales tax, levied by something over twelve thousand separate taxing jurisdictions, with rates set at state, county, city and special district level, and changing constantly.

There is no primary source that publishes them all, and a rate table one person cannot keep right is worse than no table: it looks authoritative right up to the point it costs somebody money. So this page covers the two markets where the tax is national and published, and says plainly that the third is not something it can do honestly.

For the British version of the same instrument, our VAT calculator handles the 20% and 5% rates and the domestic reverse charge, which has no equivalent in either market here.

Same tax, three names, and the names matter

VAT, GST and sales tax are the same idea: a broad tax on consumption, collected by businesses at each stage, with credit for what you paid on your own purchases. The arithmetic above is identical in every one of them.

But nobody in Australia searches for a VAT calculator and nobody in Britain searches for GST, so these are two pages rather than one with a dropdown. The difference is not cosmetic either: the UK page has to deal with a reverse charge that neither of these markets has, and this one has to deal with a province question the UK page never asks. Same maths, different forms, different words.