About TaxBackwards.ca

TaxBackwards.ca is a free Canadian reverse sales tax calculator built for bookkeepers, freelancers, sole proprietors, and small businesses. Enter a gross transaction total, select a province, and instantly extract the net pre-tax consideration and the claimable GST, HST, or QST amount.

All calculations use publicly available rates from the Canada Revenue Agency and Revenu Québec, manually verified and maintained. No accounts, logins, or user data storage — every calculation runs entirely in your browser.

TaxBackwards.ca is an arithmetic utility only and does not provide tax or accounting advice. Always verify figures against current CRA and Revenu Québec guidelines before filing.

Features

• Reverse GST/HST/QST calculations
• Auditor Precision Mode (4 decimals)
• Quebec French-Canadian formatting
• Copy-to-clipboard results
• Print-friendly ledger layout

Learn more about Ontario HST calculations and Quebec GST/QST calculations.

Official Tax References

Canadian sales tax rules are administered by the Canada Revenue Agency (CRA) for federal GST/HST and by Revenu Québec for provincial QST. Businesses should verify all filings against official government guidance. TaxBackwards.ca uses publicly available published rates from both authorities.

Province Tax Guides

Detailed reverse sales tax guides are available for currently supported jurisdictions, covering formulas, worked examples, common amounts, and ITC eligibility rules.

• Ontario HST — 13% — How to reverse-calculate Ontario's Harmonized Sales Tax and determine the ITC-eligible amount from any gross total.
• Quebec GST + QST — 14.975% — How to extract both the federal GST (5%) and the provincial QST (9.975%) from a Quebec gross total, with notes on dual-authority reporting and QST rules.