Reverse Tax Formula Canada — How It Works
When you know the tax-included total but need the pre-tax amount, you use the reverse tax formula. It works the same way across every Canadian province and territory — the only difference is the rate you divide by. This page explains the formula, shows how it applies to every province, and links to free calculators for each one.
The Formula
The reverse tax formula is:
Pre-tax amount = Total ÷ (1 + tax rate)
For example, if the total tax rate is 13% (Ontario HST):
Pre-tax = Total ÷ 1.13- Tax amount =
Total − Pre-tax
That's it. No multiplication, no separate steps. One division gives you the pre-tax amount; subtract from the total to get the tax.
Rates by Province and Territory
Canada has three tax structures — HST (single harmonized rate), GST + PST (two separate taxes), and GST only (Alberta and territories). Use the divisor that matches your province or territory:
| Province / Territory | Tax Type | Rate | Divisor |
|---|---|---|---|
| Ontario | HST | 13% | 1.13 |
| Nova Scotia | HST | 14% | 1.14 |
| New Brunswick | HST | 15% | 1.15 |
| Newfoundland and Labrador | HST | 15% | 1.15 |
| Prince Edward Island | HST | 15% | 1.15 |
| Quebec | GST + QST | 14.975% | 1.14975 |
| British Columbia | GST + PST | 12% | 1.12 |
| Saskatchewan | GST + PST | 11% | 1.11 |
| Manitoba | GST + RST | 12% | 1.12 |
| Alberta | GST only | 5% | 1.05 |
| Yukon | GST only | 5% | 1.05 |
| Northwest Territories | GST only | 5% | 1.05 |
| Nunavut | GST only | 5% | 1.05 |
Worked Example for Each Tax Structure
HST example (Ontario 13%): $226.00 ÷ 1.13 = $200.00 — tax = $26.00
GST + PST example (BC 12%): $112.00 ÷ 1.12 = $100.00 — tax = $12.00
GST only example (Alberta 5%): $105.00 ÷ 1.05 = $100.00 — tax = $5.00
GST + QST example (Quebec 14.975%): $149.75 ÷ 1.14975 = $130.25 — tax = $19.50
Use a Calculator Instead
Rather than doing the division manually, use the free province-specific calculators on TaxBackwards.ca:
- Ontario
- Quebec
- British Columbia
- Alberta
- Nova Scotia
- New Brunswick
- Newfoundland and Labrador
- Prince Edward Island
- Saskatchewan
- Manitoba
- Yukon, Northwest Territories & Nunavut
Use the free Canadian reverse tax calculator to extract tax from any total instantly.
Calculations are arithmetic estimations only and do not constitute formal tax or corporate auditing advice. All figures must be verified against current CRA guidelines before filing.