A GST-only province
Alberta
GST only at 5%
$250.00 ÷ 1.05
- Total including tax
- $250.00
- GST
- $11.90
- Price before tax
- $238.10
Alberta charges no provincial sales tax, so the only thing to back out is the 5% federal GST.
Tax tools
Reverse GST calculator.
To take GST out of a total that already includes it, divide by 1 plus the tax rate. A $105.00 Alberta receipt at 5% GST is $105.00 divided by 1.05, so the price before tax is $100.00 and the GST is $5.00.
Reverse calculator
What was the price before tax?
Type the total you actually paid. The calculator returns the pre-tax price, the federal portion and the provincial portion, and the three numbers always add back to the total you typed, to the cent.
$100.00 plus $12.00 tax is $112.00 in British Columbia.
Amount before tax$100.00
GST 5%$5.00
PST 7%$7.00
Total$112.00
British Columbia charges 12% on most goods and services.
Need to go the other way and add tax to a quoted price? Use theGST and HST calculator.
The arithmetic
How do you calculate GST from a total?
To calculate GST from a total, divide the tax-included total by 1 plus the combined tax rate for the province, then subtract the answer from the total. A $105.00 total in a 5% GST province is $105.00 divided by 1.05, which is $100.00 before tax and $5.00 of GST.
Find the divisor
The divisor is 1 plus the combined rate written as a decimal. British Columbia's combined rate is 12%, so the divisor is 1.12. Ontario's HST is 13%, so the divisor is 1.13. Quebec's combined rate is 14.975%, so the divisor is 1.14975.
Divide the total to get the base
Base equals total divided by the divisor. On a $250.00 British Columbia total, $250.00 divided by 1.12 is $223.21 before tax.
Subtract to get the tax
Tax equals total minus base. On that same British Columbia total the tax is $26.79. Never take a percentage of the total to find the tax, because the tax was charged on the base, not on the total.
Split the tax if you need the two portions
The federal portion is the base multiplied by 5%, and whatever is left of the tax is the provincial portion. On the $250.00 British Columbia total that is $11.16 of GST and $15.63 of PST. The same step works in an HST province: on a $250.00 Ontario total the federal portion is $11.06 and the provincial portion is $17.70.
The formula, in one line
Base = Total ÷ (1 + rate)
Tax = Total - Base
Federal portion = Base × 5%
Provincial portion = Tax - Federal portion
Worked examples
What does it look like on a real receipt?
The same $250.00 total, backed out in three provinces that tax three different ways. The pre-tax price is different in each one because the tax rate baked into the total is different.
An HST province
Ontario
HST at 13%
$250.00 ÷ 1.13
- Total including tax
- $250.00
- HST (federal portion)
- $11.06
- HST (provincial portion)
- $17.70
- Price before tax
- $221.24
Ontario blends both taxes into one 13% HST, so you divide once and then split the tax into its 5% federal and 8% provincial parts.
A GST plus PST province
British Columbia
GST + PST at 12%
$250.00 ÷ 1.12
- Total including tax
- $250.00
- GST
- $11.16
- PST
- $15.63
- Price before tax
- $223.21
British Columbia charges 7% PST on the price before GST, so both taxes sit on the same base and you divide by 1.12 exactly once.
Where it goes wrong
Why can't you just multiply by 0.95?
Because the tax was charged on the pre-tax price, not on the total. Three shortcuts that look reasonable and give the wrong number.
Shortcut 1
Multiplying the total by 0.95
Multiplying a $105.00 GST-included total by 0.95 gives $99.75, which implies $5.25 of GST. The correct pre-tax price is $100.00 and the correct GST is $5.00. Five percent of the base is only 4.762% of the total, which is why the shortcut always overstates the tax.
Shortcut 2
Dividing twice in a GST plus PST province
British Columbia PST is charged on the price before GST, so the 5% and the 7% both sit on the same base and you divide once by 1.12. Dividing a $250.00 BC total by 1.05 and then by 1.07 returns $222.52 instead of the correct $223.21.
Shortcut 3
Rounding the Quebec divisor to 1.15
Quebec QST is 9.975%, not 10%, so the combined rate is 14.975% and the divisor is 1.14975. On a $250.00 Quebec total the correct pre-tax price is $217.44, while a 1.15 divisor returns $217.39, a gap of $0.05 that grows with the invoice.
Every province and territory
What do you divide by in each province?
The divisor is 1 plus the combined rate. Alberta and the three territories divide by 1.05 because they charge the 5% GST alone. Prince Edward Island divides by 1.15 because its HST is 15%.
| Province or territory | Tax type | Combined rate | Divide the total by | Tax fraction |
|---|---|---|---|---|
| British Columbia | GST + PST | 12% | 1.12 | 12 / 112 |
| Alberta | GST only | 5% | 1.05 | 5 / 105 |
| Saskatchewan | GST + PST | 11% | 1.11 | 11 / 111 |
| Manitoba | GST + RST | 12% | 1.12 | 12 / 112 |
| Ontario | HST | 13% | 1.13 | 13 / 113 |
| Quebec | GST + QST | 14.975% | 1.14975 | 14.975 / 114.975 |
| New Brunswick | HST | 15% | 1.15 | 15 / 115 |
| Nova Scotia | HST | 14% | 1.14 | 14 / 114 |
| Prince Edward Island | HST | 15% | 1.15 | 15 / 115 |
| Newfoundland and Labrador | HST | 15% | 1.15 | 15 / 115 |
| Yukon | GST only | 5% | 1.05 | 5 / 105 |
| Northwest Territories | GST only | 5% | 1.05 | 5 / 105 |
| Nunavut | GST only | 5% | 1.05 | 5 / 105 |
Rates verified July 2026 against federal and provincial government sources. The tax fraction is the shortcut the Canada Revenue Agency publishes: multiply a tax-included total by the fraction to get the tax without finding the base first.
Reverse GST questions
The questions people actually ask.
How do you calculate GST from a total in Canada?
To calculate GST from a tax-included total in Canada, divide the total by 1 plus the combined tax rate for that province, then subtract the result from the total. In a 5% GST province such as Alberta, $105.00 divided by 1.05 is $100.00 before tax and $5.00 of GST. In Ontario, where HST is 13%, you divide by 1.13 instead.
What is the reverse GST formula?
The reverse GST formula is base = total divided by (1 + rate), and tax = total minus base. The rate is the combined rate for the province, so the divisor is 1.05 in Alberta, Yukon, the Northwest Territories and Nunavut, 1.12 in British Columbia and Manitoba, 1.13 in Ontario, 1.14 in Nova Scotia, 1.14975 in Quebec, and 1.15 in New Brunswick, Newfoundland and Labrador and Prince Edward Island.
How do you back 5% GST out of a price?
To back 5% GST out of a price, divide the tax-included amount by 1.05. On a $105.00 receipt that gives $100.00 before tax and $5.00 of GST. Multiplying the total by 0.95 gives $99.75 instead, which is wrong, because the 5% was charged on the smaller pre-tax figure and not on the total.
How do you split an HST total into the federal and provincial parts?
To split an HST total, divide the total by 1 plus the HST rate to get the base, multiply the base by 5% for the federal part, and treat the remainder as the provincial part. On a $250.00 Ontario total at 13% HST, the base is $221.24, the federal part is $11.06 and the provincial part is $17.70. Multiplying the $250.00 total by 5% would give $12.50, which overstates the federal part.
Do you divide by 1.05 and then by 1.07 in British Columbia?
No. In British Columbia you divide a tax-included total once by 1.12, because BC PST is charged on the price before GST, so the 5% GST and the 7% PST both apply to the same base. On a $250.00 BC total, one division by 1.12 gives $223.21 before tax, while dividing by 1.05 and then by 1.07 gives $222.52 and understates the price.
What do you divide by in Quebec?
In Quebec you divide a tax-included total by 1.14975, because Quebec charges 5% GST plus 9.975% QST on the price before GST, for a combined 14.975%. On a $250.00 Quebec total that gives $217.44 before tax. Rounding the divisor to 1.15 returns $217.39, which is off by $0.05 on a total this size and drifts further on a large invoice.
What tax fraction does the CRA use to find the tax in a total?
The CRA tax fractions are 5/105 for the 5% GST, 13/113 for Ontario HST at 13%, 14/114 for Nova Scotia HST at 14%, and 15/115 for the 15% HST provinces. Multiplying a tax-included total by the fraction gives the tax directly, so $250.00 times 13/113 is $28.76 of Ontario HST, the same answer as dividing by 1.13 and subtracting.
Before you file it
This calculator is an estimate, not tax advice. Verify anything you are filing with the Canada Revenue Agency or your accountant.
Adding tax to a quote instead? Use the GST and HST calculator. Not registered yet? Read the GST number guide.