Income Tax Withholding

Definition

Income tax withholding is the employer's obligation, under Income Tax Act s.153(1)(a), to deduct federal and provincial income tax from each payment of remuneration and remit it to CRA before the employee receives the net amount. The goal is to approximate the employee's annual tax liability in small installments, so that the T1 assessment results in a small refund or balance owing rather than a large year-end surprise.

Key rules

• CRA publishes province-specific withholding tables in Guide T4032 and the underlying formulas in Guide T4127. Most payroll software uses the T4127 formulas so that it can handle non-standard pay frequencies.
• The withholding base is taxable remuneration: gross wages plus most taxable benefits, less RPP and RRSP contributions collected at source, union dues, and any approved T1213 deduction.
• Provincial tax follows the province of employment (the employer's permanent establishment where the employee reports), not the employee's residence, with the narrow exception of employees who work from home full time.
• Bonuses and retroactive pay use the "bonus method": annualize the regular salary, compute tax, then compute tax on the annualized salary plus bonus. The difference times the pay frequency is the withholding on the bonus.
• Withholding is in addition to CPP and EI, not a replacement. The three are combined on a single PD7A.

Example

A salaried employee in British Columbia earns $5,000 per bi-weekly cheque (26 pays), has filed TD1 and TD1BC with only the basic personal amounts, and contributes $250 per cheque to a group RRSP through source deductions in 2026.

1. Annualized taxable earnings: ($5,000 − $250) × 26 = $123,500.
2. Using the T4127 formulas for BC, compute federal tax and BC tax on $123,500 less the 2026 basic personal amounts (federal and BC) times the lowest-bracket rates.
3. Divide the annual total by 26 to get the bi-weekly withholding, which flows into the PD7A along with CPP and EI.

In practice, the calculation is left to payroll software configured with T4127, but reviewing the formula by hand once a year catches TD1 misentries that compound all year.

Common mistakes

• Using last year's T4032 tables into the new calendar year. Brackets and basic amounts change every January 1.
• Withholding on the employee's home province instead of the province of the employer's establishment, which causes provincial mismatches on T1.
• Applying the bonus method to overtime or vacation pay. Those are ordinary wages, not bonuses.
• Ignoring CRA letters of authority (issued after a T1213 deduction request), so the employee over-withholds even though CRA has permitted a reduction.
• Treating shareholder draws as non-remuneration. If the draw is paid as salary through payroll, it is subject to withholding and appears on a T4 (see salary vs. dividends).

Related concepts

The withholding base is shaped by the TD1 form. Income tax combines with CPP and EI on every pay cycle and is remitted with a PD7A. Totals show up in Box 22 of the T4 slip.