How do I remove 13% tax from a total in Ontario?

Divide by 1.13. A $100.00 total is $88.50 before tax and $11.50 of tax. Subtracting 13% from the total instead gives $87.00, which is wrong by $1.50.

Why is subtracting the percentage wrong?

Because the tax was calculated on the pre-tax price, not on the total. Taking 13% off the total removes 13% of a bigger number than the one the tax was worked out on, so you take away too much. The error is proportional and grows with the receipt.

Does this work for a receipt with exempt items on it?

No, and that is the real limitation. If part of the bill was zero-rated — groceries, prescriptions — the tax was charged on only part of the total, and dividing the whole thing gives the wrong split. This works for a receipt where everything was taxable.

2026 · 13 jurisdictions · from total to base

Reverse sales tax calculator

You have the total and you need the price before tax. The answer is a division, not a subtraction — and getting that backwards is the commonest arithmetic mistake on an expense claim.

Written and edited by Pablo Ruiz QuinteroSources checked September 1, 2026Rates read off the CRA and Revenu Québec on 2026-09-07

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Total you were charged

Province or territory

Ontario charges a single harmonised 13% HST. Adding 5% GST to it — a common mistake — double-counts the federal share.

Price before tax

$88.50

from $100.00 charged

The breakdown
Price before tax	$88.50
HST 13%	$11.50
Total	$100.00

Combined rate 13%. The HST replaces the GST rather than adding to it: the federal 5% is already inside that figure.

Why you cannot just subtract 13%

You have a receipt for $100.00 in Ontario and you need the price before tax. The instinct is to take 13% off the total. That gives $87.00, and it is wrong by $1.50.

The reason is that the tax was never calculated on $100.00. It was calculated on the smaller number — the pre-tax price — and then added. So to undo it you divide by 1.13, not subtract a percentage. The right answer is $88.50 before tax and $11.50 of tax.

The error is proportional, so it grows with the receipt: on $10,000 it is $149.56. It is the single most common arithmetic mistake in expense claims, and it always goes the same way — understating the pre-tax cost, and therefore the tax you could claim back.

When you actually need this

Expense claims and bookkeeping. A business reclaims the GST/HST it paid as an input tax credit, and to do that it needs the tax split out. A till receipt that only shows a total forces the calculation.

Invoicing backwards from a round number. Quoting "$1,000 all in" means the price before tax is $884.96, not $1,000. Get that wrong on a quote and the difference comes out of your margin.

Checking a receipt. Dividing the total and comparing the tax line is the fastest way to spot a till charging the wrong rate — which happens most often in the months after a rate change.

The arithmetic, in full

For Ontario, with a combined rate of 13%:

Price before tax = total ÷ 1.13

HST = price before tax × 0.13

Worked on $100.00: $100.00 ÷ 1.13 = $88.50, of which $11.50 tax.

There is only one tax to reverse here, which makes Ontario the easy case.

Where to go next

Reverse QST calculator (Quebec)Two taxes on one base — reversing them in sequence is wrong.Reverse HST calculator (Ontario)One division by 1.13.Add sales tax insteadThe same tool the other way round.All Canadian calculatorsIncome tax by province, and everything else.

Questions

How do I remove 13% tax from a total in Ontario?: Divide by 1.13. A $100.00 total is $88.50 before tax and $11.50 of tax. Subtracting 13% from the total instead gives $87.00, which is wrong by $1.50.
Why is subtracting the percentage wrong?: Because the tax was calculated on the pre-tax price, not on the total. Taking 13% off the total removes 13% of a bigger number than the one the tax was worked out on, so you take away too much. The error is proportional and grows with the receipt.
Does this work for a receipt with exempt items on it?: No, and that is the real limitation. If part of the bill was zero-rated — groceries, prescriptions — the tax was charged on only part of the total, and dividing the whole thing gives the wrong split. This works for a receipt where everything was taxable.