Reverse HST Calculator — pull the tax out of any total
Enter a tax-included amount and get back the pre-tax price and the exact HST — the two numbers your bookkeeping, expense claims, and input tax credits actually need. Works for every province's taxes, not just HST.
The reverse formula, and the mistake to avoid
The correct method is total ÷ (1 + rate): a $1,000 Ontario receipt is $1,000 ÷ 1.13 = $884.96 before tax, with $115.04 of HST. The classic error is taking 13% of the total — $130.00 — which overstates the tax by $14.96, because HST was charged on the smaller pre-tax base, not on itself. Over a year of expense entries, that error compounds into a real misstatement of your input tax credits.
Reverse divisors by province
| Province | Tax | Divide the total by |
|---|---|---|
| Ontario | 13% HST | 1.13 |
| Nova Scotia | 14% HST | 1.14 |
| NB · NL · PEI | 15% HST | 1.15 |
| Quebec | 5% GST + 9.975% QST | 1.14975 |
| British Columbia | 5% GST + 7% PST | 1.12 |
| Alberta · Territories | 5% GST | 1.05 |
Where reverse calculation earns its keep
Expense reports built from tax-included receipts. Input tax credit claims, where only the tax portion is refundable. Contracts and quotes agreed “tax included,” which still must be invoiced with the tax broken out. Mileage and per-diem reconciliations. Any e-transfer that arrived as one round number. In each case the total is known and the split is not — reverse calculation recovers it exactly, to the cent.
From “tax included” to a proper invoice
If a client agreed to a tax-included price, your invoice still needs the pre-tax line and the HST shown separately — with your registration number, per the CRA's requirements. Reverse the total above, then tap “Create an invoice with this tax”: the free generator opens with your province's tax applied, so entering the recovered base rebuilds the agreed total exactly.
Frequently asked questions
How do I calculate HST backwards from a total?
Divide the tax-included total by 1 plus the rate. In Ontario, divide by 1.13: a $113.00 total becomes $100.00 before tax, and the $13.00 difference is the HST. Use 1.14 for Nova Scotia and 1.15 for New Brunswick, Newfoundland and Labrador, and PEI.
What is the reverse HST formula?
Pre-tax amount = total ÷ (1 + rate). HST = total − pre-tax amount. For a $1,000 Ontario receipt: $1,000 ÷ 1.13 = $884.96 before tax, and $115.04 of HST. A common mistake is multiplying the total by 13% instead — that overstates the tax, because the 13% was charged on the smaller pre-tax base.
Why would I need to extract HST from a total?
Mostly bookkeeping: expense claims, input tax credits, and accounting entries need the tax split out, but many receipts, contracts, and e-transfer amounts only show the tax-included total. Reverse calculation recovers the exact HST you paid so you can claim it back.
Can I claim the HST I extract as an input tax credit?
If you are GST/HST-registered and the expense was for your commercial activity, generally yes — that recovered HST is exactly what input tax credits refund. Keep the receipt: for purchases of $100 or more it must show the supplier's registration number for the credit to hold up.
Does this work for GST and QST too, not just HST?
Yes. Pick any province above: the calculator divides by the right combined factor — 1.05 for GST-only provinces, 1.12 for BC's GST+PST, 1.14975 for Quebec's GST+QST — and splits each tax onto its own line from the recovered base.
My contract price is “HST included.” How do I invoice that?
Reverse the total first: for a $5,000 tax-included Ontario contract, the pre-tax price is $4,424.78 and the HST is $575.22. Your invoice shows $4,424.78 as the line amount and 13% HST on top, arriving back at exactly $5,000.00 — use “Create an invoice with this tax” above to set it up.
Which rate do I use for an out-of-province receipt?
Use the rate of the province where the purchase happened or was delivered — that's the rate the seller charged under the place-of-supply rules. A hotel bill from Halifax reverses at 14%, a Toronto one at 13%, a Calgary one at 5% GST.