Reverse Sales Tax Calculator (Canada)

Reverse sales tax divisors for every province

To reverse sales tax, divide the tax-included total by the divisor for your province; the result is the price before tax, and the difference is the tax. The last column shows what share of any tax-included total is tax. It is always smaller than the headline rate, because the rate is a percentage of the pre-tax price, not of the total.

Reverse HST, GST, PST and QST: worked examples

Here is the reverse tax calculator’s arithmetic for the four main systems, using the same engine as the tool above.

• Reverse HST (Ontario): $226.00 ÷ 1.13 = $200.00 before tax; HST is $26.00.
• Reverse GST and QST (Quebec): $114.98 ÷ 1.14975 = $100.00; GST $5.00 and QST $9.98. Both are worked out on the pre-tax price.
• Reverse GST and PST (British Columbia): $56.00 ÷ 1.12 = $50.00; GST $2.50 and PST $3.50.
• Reverse GST (Alberta and the territories): $52.50 ÷ 1.05 = $50.00; GST $2.50.

Why subtracting the tax rate gives the wrong answer

Subtracting the tax rate from a total takes the percentage of the wrong number. Take an Ontario invoice for $1,130.00. Knocking 13% off gives $983.10, but the real pre-tax price is $1,000.00 – the shortcut is out by $16.90. The tax was 13% of $1,000.00, not 13% of $1,130.00.

The error grows with the rate and the amount. In New Brunswick (15% HST) the same shortcut on a $10,000.00 total understates the price by $195.65. That is enough to throw off a quote, an expense claim or a bookkeeping entry.

Splitting HST into its federal and provincial parts

Sometimes you need to know the federal and provincial shares separately, for example to check an Ontario point-of-sale rebate or to report a cross-border purchase. The HST is always the 5% federal rate plus the provincial part, so each share is its rate divided by 1 plus the HST rate.

In Ontario the federal 5% is total × 5 ÷ 113 and the provincial 8% is total × 8 ÷ 113. On a $226.00 total that gives $10.00 federal and $16.00 provincial. In Quebec there is nothing to split, because the GST and QST already appear on separate lines of the receipt.

Receipts that mix taxed and untaxed items

Do not reverse a whole grocery or pharmacy receipt with a single divisor. Zero-rated items (basic groceries, prescription drugs), exempt services and rebated items are mixed in with fully taxable ones, so the receipt total is not "price × (1 + rate)".

Reverse only the taxable lines, or better, read the tax from the receipt. In Ontario, items that qualify for the point-of-sale rebate (children’s clothing, diapers, books and prepared food of $4.00 or less) carry only the 5% federal part, so their divisor is 1.05, not 1.13. In British Columbia a restaurant bill carries GST but no PST, so you reverse it at 5% unless it includes liquor or soda.

Rounding: why your answer may be a cent off

Reverse calculations rarely land on round cents, and sellers round tax on each line or on the whole invoice. A one- or two-cent difference from the receipt is normal; the CRA says the same of its own GST/HST calculator.

Revenu Québec sets explicit rules for registers: a fraction of half a cent ($0.005) or more is rounded up to a whole cent, and the GST and QST may be worked out on the total of all items before rounding. A register that cannot handle three decimals may use 9.97% or 14.97%, so a Quebec receipt can differ slightly from an exact 14.975% reverse calculation.

Reverse tax for bookkeeping and input tax credits

GST/HST-registered businesses often need the reverse calculation to claim input tax credits (ITCs) from receipts that show only a tax-included total. The CRA’s documentation rules depend on the size of the purchase:

• Under $100: the supplier’s name, the date and the total paid are enough; the receipt does not have to show the tax separately.
• $100 to $499.99: the receipt must also show the supplier’s GST/HST registration number and either the GST/HST charged or a statement that the price includes GST/HST at the applicable rate – the case where you reverse the total yourself.
• $500 or more: add the buyer’s name, a brief description of what was bought and the payment terms.