How to Calculate GST/HST: Add or Remove Tax by Hand

To calculate GST or HST by hand, multiply the price before tax by the applicable rate. To recover the pre-tax price from a tax-included total, divide by one plus that rate. First determine whether the supply is taxable and which rate applies. The GST/HST calculator can perform ordinary add-and-remove calculations; the examples below explain the arithmetic.

Calculate tax added to a price

Tax = pre-tax price × tax rate. Add that amount to the price. For a $100 taxable sale at Ontario’s 13% HST, the tax is $13 and the total is $113. At Nova Scotia’s 14% rate, the same pre-tax price produces $14 HST and a $114 total. Federal GST and HST rates depend on the place of supply and transaction; see the CRA rate table.

Remove tax from a total

Pre-tax price = total ÷ (1 + rate). Tax is the total minus the pre-tax price. For a $113 Ontario total that includes 13% HST, $113 ÷ 1.13 = $100 and the HST is $13. Subtracting 13% of $113 gives the wrong answer because the tax rate applies to the price before tax.

Applicable rate	Divide the tax-included total by	Example total → pre-tax price
5% GST	1.05	$105 → $100
13% HST	1.13	$113 → $100
14% HST	1.14	$114 → $100
15% HST	1.15	$115 → $100

Rounding individual invoice lines can make a cent of difference. See the reverse-tax guide for more examples.

GST with a separate provincial tax

British Columbia and Manitoba generally have a 7% provincial sales tax, while Saskatchewan generally has a 6% PST. On an ordinary $100 sale where GST and the respective general provincial rate both apply to the same pre-tax base, GST is $5; PST or RST is $7 in BC or Manitoba and $6 in Saskatchewan. The totals are $112 or $111 respectively. GST and the provincial tax are separate obligations. Check exemptions and the particular purchase before applying both rates. See the GST and PST calculator and provincial tax overview.

Special cases need a different calculation. In BC, for example, the CRA explains that GST on a taxable vapour product is calculated on the price including its 20% PST. The ordinary 12% combined shortcut is not suitable. See CRA’s explanation of GST and BC vapour-product PST and the BC Provincial Sales Tax Act.

Calculate GST and QST in Quebec

For a taxable Quebec sale where both taxes apply, calculate 5% GST and 9.975% QST on the same pre-tax price. On $100, GST is $5.00 and QST is $9.975, which rounds to $9.98 for a $114.98 total. To reverse a combined total before rounding, divide by 1.14975; reversing rounded tax lines can differ by a cent. See the Quebec calculator and Quebec tax guide.

Which rate goes on the invoice?

Use the rate for the taxable supply under the applicable place-of-supply rules; do not assume every sale is taxable simply because a calculator displays a rate. Some supplies are zero-rated or exempt and provincial taxes have their own rules. The place-of-supply guide and exempt versus zero-rated guide explain the distinction.

Show tax and supporting information as required for the transaction. See what to show on a GST/HST invoice and CRA input tax credit documentation.

Does the tax amount equal what a business remits?

Not necessarily. A registrant using the regular method generally accounts for GST/HST collected or collectible, eligible input tax credits and adjustments. The Quick Method has separate eligibility and remittance-rate rules. See input tax credits and the Quick Method.

Sources

Sources checked October 17, 2026.