Exactly which official source backs every number on this site, and what's still honestly incomplete.
Every calculator on this site is checked against a primary, official source before it goes live — not a secondary blog post or aggregator site. Where we found genuine disagreement between sources during research, or where full coverage isn't there yet, that's disclosed directly below rather than hidden. This page exists so that claim can actually be verified, not just taken on trust.
Tax year 2026 brackets and standard deductions from IRS Revenue Procedure 2025-32, the same document the IRS itself publishes each year to set the following year's inflation-adjusted figures. Verified against multiple independently published worked examples before use.
IRS.gov source →All 9 no-income-tax states and all genuinely flat-rate states are fully verified. Graduated-bracket states were sourced from the Tax Foundation's annual report, cross-checked against each state's own published cumulative-tax formula where available (for example, California and New York were verified to the cent against their own tax authorities' worked examples). Roughly 15 states use single-filer brackets as an approximation regardless of the filing status selected, since married-filing brackets differ from single brackets in those states and weren't fully modeled — this is disclosed directly in the calculator's result for any affected state.
2026 rates, wage base, and Additional Medicare Tax threshold cross-referenced against multiple independent payroll and CPA-published sources before use.
2026 federal brackets and Basic Personal Amount, including the BPA phase-out range for higher incomes, sourced directly from the Canada Revenue Agency's own published figures.
Canada.ca source →12 of 13 provinces and territories use official 2026 bracket rates published directly by the CRA. Two honest gaps: these figures don't yet include each province's own basic-personal-amount-equivalent credit (meaning real amounts owed are likely somewhat lower, especially at lower incomes), and Ontario and Prince Edward Island's additional provincial surtax isn't included. Quebec is intentionally left unavailable — it's administered separately by Revenu Québec on a genuinely different tax base, not just different numbers, and building it correctly requires dedicated verification we haven't completed yet. The federal 16.5% Quebec abatement is correctly applied to the federal estimate when Quebec is selected, even though the provincial portion itself isn't shown.
2026 contribution rates and maximum pensionable/insurable earnings cross-referenced against multiple independent Canadian payroll sources before use.
These calculations use the same standard formulas taught in financial mathematics and used industry-wide by lenders and financial institutions — the fixed-payment amortization formula, the compound interest formula with periodic contributions, and their mathematical inverses (solving for time-to-payoff or required contribution instead of payment). These aren't sourced from a single external site; they're verified through internal consistency checks — for example, confirming that solving for a payoff time and then feeding that time back into the original payment formula returns the original payment, to the cent.
Tax figures change annually. The IRS typically publishes the following year's figures in October or November; the CRA follows a similar autumn schedule. We review and update the tax calculators against newly published figures each year once they're officially released, and every tax page shows a "last verified" date so you can see at a glance how current the numbers are.