PayNorth implements the CRA's published T4127 Payroll Deductions Formulas (Option 1, annualized) for Ontario, for supported situations: federal and Ontario income tax (including the Ontario surtax, health premium and tax reduction), CPP, CPP2 and EI, with annual maximums applied automatically. Statutory data lives in one versioned table in the engine; no rate or threshold is hard-coded anywhere else.
Per-component rounding, half-up at two decimals (CPP, CPP2, EI and per-period tax are each rounded, then totalled), with annualized income carried unrounded until the end — the T4127 approach. Displayed lines always sum exactly to displayed totals; PDFs print the stored numbers, never a reformatted copy. Differences of a cent or two against CRA's PDOC can occur where the formula and table methods round differently; differences beyond that are treated as defects.
Every finalized statement permanently records: the app version, the calculation-engine version, the CRA formula edition and its effective date (chosen by the pay date — never by today's date), the province, a checksum of the exact rate table used, and the calculation timestamp. Finalized statements are never edited or recalculated: corrections are made by voiding (audit-trailed) or void-and-redo, which creates a linked replacement. Pay dates in years PayNorth doesn't have CRA data for are refused rather than approximated.
The CRA's own Payroll Deductions Online Calculator (PDOC) is free and supports prior years. Run any employee through both — we encourage it, especially your first payday. If you find a material difference, email hello@pay-north.ca with both results (no employee names needed): calculation reports get fixed ahead of everything else, and confirmed corrections appear in the history below.
| Date | Engine | Formula editions | Notes |
|---|---|---|---|
| 2026-07-11 | 2026.07.1 | CRA-T4127-122+123 (2026) · CRA-T4127-119/121-PROV (2025) | Formula-version records added to all finalized statements. Cent-safe rounding fix (half-cent premiums now round up per CRA instruction). Statement federal/Ontario tax lines follow the computed T1/T2 allocation. 2025 pay dates supported (provisional, verify-with-PDOC notice). Weekly-53 and bi-weekly-27 pay schedules added. Unknown years now refused instead of approximated. |
| 2026-07-11 | — | CRA-T4127-122+123 | Initial public release: CRA T4127 2026 editions (federal + Ontario), CPP/CPP2/EI with maximums, Ontario surtax, health premium and tax reduction; Ontario minimum-wage warnings incl. the Oct 1, 2026 increase. |
The CRA publishes new T4127 editions effective January 1 and July 1; Ontario's minimum wage typically changes October 1. Each edition ships as a new versioned data block — prior editions are kept forever so historical statements always show the rules that produced them. Every update passes the full test suite, and material calculation changes receive external review, before release.
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