GST/HST math trips up more Canadian small-business owners than almost any other bookkeeping task. Not because it's hard — the arithmetic is grade-school — but because the rules around the arithmetic shift based on your province, your customer's province, and whether you're reading a quote or a receipt. This guide walks through exactly how to do it for 2026, with real examples.
Every province charges the same 5% federal Goods and Services Tax (GST). What sits on top depends on where the sale actually happens:
This is the invoicing case: you know what you want to charge, and you need to add the sales tax on top.
Total = Pre-tax price × (1 + combined rate)
Total = $100 × 1.13 = $113.00
The $13 tax is the HST. On the invoice you show one line: "HST 13%: $13.00."
GST = $100 × 0.05 = $5.00
QST = $100 × 0.09975 = $9.98
Total = $114.98
Quebec is unique: since 2013, QST is calculated on the same pre-tax base as GST (not on the GST-inclusive amount). You show GST and QST as two separate lines on the invoice.
GST = $100 × 0.05 = $5.00
PST = $100 × 0.07 = $7.00
Total = $112.00
Both GST and PST apply to the pre-tax price in parallel. A common mistake is calculating PST on the GST-inclusive $105 — that gives $112.35, which is wrong.
This is the bookkeeping case: you're looking at a $113 receipt from an Ontario purchase and need to know how much was pre-tax vs. how much was tax.
Pre-tax = Total ÷ (1 + combined rate)
Pre-tax = $113 ÷ 1.13 = $100.00
Tax = $113 − $100 = $13.00
Do not multiply the total by 0.87 to remove Ontario HST. It looks close but gives $98.31 instead of $100. The correct math is always to divide by (1 + rate), not to subtract a percentage.
Our GST/HST Calculator handles both add-tax and remove-tax modes for every Canadian province — including Quebec's QST and the BC/Saskatchewan/Manitoba PST rules.
Open the calculatorCharge the sales tax of the destination province, not your own. If you're an Ontario freelancer invoicing a BC client, you charge 5% GST — not 13% Ontario HST. Getting this wrong means credit notes, refunds, and CRA paperwork later.
For physical goods, the destination is where the item is delivered. For services, it's generally where the customer is located. For digital services (software, subscriptions), it's the customer's address on file. The CRA's Place of Supply Rules get more detailed for specific industries — but for most freelancers, "where does my customer live?" is the right question.
You must register once your worldwide taxable revenues exceed $30,000 in any single calendar quarter or in four consecutive calendar quarters. Below that, you're a "small supplier" and registration is voluntary.
Should you register voluntarily under the threshold? It depends:
If you're looking at older invoices or receipts, remember that Nova Scotia reduced its HST from 15% to 14% effective April 1, 2025. The provincial portion dropped from 10% to 9%; the 5% federal GST stayed the same. Anything before that date used 15%, and CRA published transitional rules for supplies straddling the change.
The math for GST/HST is simple: multiply by (1 + rate) to add tax, divide by (1 + rate) to remove it. The complexity is in the rules around it — which rate applies, which province wins the place-of-supply question, and whether you need to register in the first place. Once you know your combined rate, everything else is arithmetic.