Calculation Methodology

What each calculator must explain

A calculator is a model of a defined question, not a complete assessment of someone’s finances. Each tool needs to identify its purpose, supported jurisdiction, relevant period, inputs and units. Dollar amounts are Canadian dollars unless another currency is stated.

The result must distinguish a statutory calculation from an assumption-based projection. Its explanation needs to tell you which circumstances are outside the model and when professional advice or an official determination is needed.

Rate tables and effective dates

Statutory rates and thresholds are kept separate from user inputs and forecasting assumptions. Each supported rate set needs an official source and an effective date. A prior-year figure must not silently become a current-year figure.

The official-source directory identifies starting points. Each tool must cite the specific table or rule it uses; a general link to a government homepage is not sufficient evidence for a particular numerical threshold.

Explain the model

• Tax tools: describe marginal tiers, deductions, credits, eligibility assumptions and any exclusions.
• Mortgage tools: state compounding, payment frequency, term, amortization, fees and any insurance treatment.
• Growth tools: state return assumptions, contribution timing, taxes, fees and inflation treatment.
• Benefit and retirement tools: state eligibility assumptions, payment period and limits on the estimate.

Precision and rounding

Use a documented precision and rounding approach. Keep intermediate calculations sufficiently precise, then round displayed currency appropriately. A displayed total may differ slightly from the sum of rounded components. Where official instructions prescribe a rounding method, follow it for the supported calculation.

Numerical checks before a tool is published

Our release standard requires checks of known examples, zero and invalid inputs, threshold boundaries and relevant jurisdictional differences. Where an official worked example is available, it provides a reference for comparison.

For example, a marginal tax model needs checks just below, at and just above a bracket boundary. A periodic-payment model needs checks of payment timing and compounding conventions. These are examples of required checks, not claims that an unpublished tool has passed them.

A page may describe a completed test or audit only when the work and its scope can be supported. Model changes require a fresh check of the affected cases.

Limits of projections

Assumed returns are not forecasts or guarantees. Future legislation, inflation, rates and personal circumstances can change outcomes. An estimate cannot establish eligibility, lender approval, a tax assessment or an entitlement to a benefit. Read the specific tool notes and the Disclaimer.

Raise a methodology question

Send the tool URL, relevant date, jurisdiction and a non-sensitive example to [email protected].