Methodology

1. Primary sources only

We take each figure from the body that sets it. Federal tax, CPP and EI come from the Canada Revenue Agency. Quebec tax, QPP and QPIP come from Revenu Québec and Retraite Québec. Provincial brackets and credits come from each province's or territory's finance ministry. Insurance premiums come from CMHC. Mortgage rules come from OSFI and the Department of Finance. Interest rates come from the Bank of Canada. We do not copy from banks, blogs or other calculators. When two official pages disagree, we follow the one used for real payroll or filing and note the conflict in the data file.

2. Payroll formulas, not approximations

The take-home pay calculator follows the CRA's T4127 Payroll Deductions Formulas. That is the document Canadian payroll systems use. It covers the enhanced CPP deduction, the base CPP and EI credits, the Ontario surtax and health premium, provincial tax reductions and the Quebec abatement. Quebec tax follows Revenu Québec's TP-1015.F. Mortgage math uses the semi-annual compounding required by section 6 of the Interest Act.

3. Versioned data with provenance

Each annual figure lives in a data file for its tax year. The file records the source name, its URL and the date we last checked it. Nothing is typed into a page by hand. Key facts, worked examples and source lists are built from those files, so they cannot drift from the calculations. When January figures arrive, we add a new year file and keep the old one.

4. Tests against hand-worked official examples

The calculation engine has no interface code and is covered by automated tests. Each test works an example by hand from the official formula. Examples include a $60,000 salary in each province, CPP at the ceiling, and a $100,000 mortgage at 5% over 25 years. The engine must match to the cent. The site cannot be published if a test fails.

5. Re-verification

An automated check confirms that each figure has a source, each source link works, and no data file goes unchecked for too long. A separate review re-reads each source and compares the figures. The founder also spot-checks results against the CRA's payroll calculator and bank calculators. Changes go on the changelog.

6. What we deliberately leave out

Each tool page lists what it does not model. We would rather give a correct number with clear limits than a vague one that claims to cover every case. When an answer depends on an assumption, such as your tax rate in retirement, that assumption is an input you can change. It is never a hidden constant.

Corrections

If you find an error, contact us. We fix confirmed errors within days and record them in the changelog with the date and the change. See the editorial policy.

Written and maintained by Nishant Malik, founder of GlassLayer.