ERPNext ships a capable payroll engine — Salary Structure, Salary Component, Payroll Entry, Salary Slip — but it is deliberately country-agnostic. Nothing in core knows that CPP has a yearly maximum pensionable earning and a basic exemption prorated over pay periods, that EI insurable earnings stop at an annual ceiling with a separate employer multiplier, or that federal and provincial tax must be computed from CRA's payroll deduction formulas using TD1 and TD1-XX claim amounts. Canadian finance teams end up re-keying ERPNext gross pay into a separate payroll bureau, then reconciling two sets of numbers at year end — and rebuilding T4 slips by hand in a spreadsheet, because ERPNext has no T4, T4A, ROE or PD7A concept at all. The cost is not the data entry; it is the February scramble when a T4 box does not tie to the general ledger.

The Canada Payroll & T4 Pack is a proper Frappe app (ecosire_ca_payroll) with its own module, installed alongside ERPNext rather than patching it. Statutory rates live in versioned DocTypes — CA Payroll Year holds the CPP rate, basic exemption, YMPE, EI rate, employer multiplier and MIE for a tax year, with child tables for the federal and each provincial bracket set — so a new year is a data change, not a code deploy. Employee-side inputs sit on CA Employee Tax Credit (TD1 federal and provincial claim amounts, CPP/EI exemption flags, additional tax requested, prescribed zone deduction). Calculation hooks into the standard Salary Slip lifecycle via hooks.py doc events on validate and on_submit, so deductions appear as ordinary Salary Components and post through ERPNext's existing accounting entries — CPP employee, CPP employer, EI employee, EI employer and income tax each map to their own payable account, which is what makes the T4 reconcile back to the trial balance.

Year-to-date control is what actually makes Canadian payroll correct, so the app maintains a CA YTD Ledger per employee, per payroll account and per year, updated inside the same transaction as Salary Slip submission and reversed on cancel. That ledger is the single source for maximum-contribution caps, for CPP prorating when an employee turns 18 or 70 mid-year, and for the year-end forms. CA T4 Slip and CA T4A Slip are generated from it with box-level mapping (boxes 14, 16, 18, 22, 24, 26, 44, 46, 52 and the other-information boxes), amended and cancelled slip states, CRA-schema XML for electronic filing, and per-employee PDF slips rendered from Frappe print formats. CA T4 Summary reconciles slip totals against what was actually remitted. CA Record of Employment assembles insurable hours and the required pay-period earnings history for the reason and last-day-worked entered by HR. CA Remittance Summary produces PD7A figures per remitting period with a drill-down to the contributing slips, and bank output is generated as CPA Standard 005 direct-deposit files with configurable originator and institution settings.

Everything is reachable programmatically: whitelisted methods and the standard Frappe REST API expose slip generation, YTD lookups and remittance figures, so a portal or scheduled integration can consume them without screen-scraping. A scheduler event runs a nightly YTD reconciliation and flags any employee whose contributions have drifted from the recomputed value. Permissions ship as role profiles — Payroll Officer, Payroll Manager, Payroll Auditor — with field-level restrictions on the tax-credit DocType and read-only slip visibility for employees through the portal. Client scripts add the in-form validations that stop bad data early: a TD1 amount below the basic personal amount, a missing SIN, an ROE raised for an employee with no submitted slips in the period. The app targets Frappe/ERPNext v15 and v16 and is built against your actual bench and your existing Salary Structures.

This is build-to-order, not a marketplace download. You request a quotation, we run a short scoping call to confirm your provinces, pay frequencies, salary component layout, chart of accounts and bank, and we then build against your version. Typical delivery is one working week from confirmed scope. You receive installable source code for your version, a staging deployment for UAT with a parallel run against your last real pay period, a documented rollback plan, and a private git repository handed over at go-live so you are never locked to us.