T4 Preparation Checklist: A Step-by-Step Guide for Ontario Employers

T4 season arrives every February, and for Ontario small business owners, it can feel like a scramble. T4 slips must be distributed to employees and filed with the CRA by the last day of February each year — and the penalties for late or incorrect T4s can be surprisingly large. This checklist walks you through the entire process.

Who Must File T4 Slips

You must file T4 slips for every person from whom you deducted income tax, CPP, or EI premiums during the year — or who earned more than $500 in employment income from you, even if no deductions were made.

• All regular employees, regardless of income amount if deductions were taken
• Employees earning more than $500 even with no deductions
• Employees who worked any part of the year, even if terminated
• Shareholders who received salary (not dividends — those go on T5 slips)

Key T4 Boxes You Must Complete

Most employers only need to complete a subset of the 80+ boxes on a T4. Here are the essential boxes for a typical Ontario employment situation.

• Box 14 — Employment income: total gross pay including salary, wages, bonuses
• Box 16 — Employee's CPP contributions
• Box 18 — Employee's EI premiums
• Box 22 — Income tax deducted
• Box 26 — CPP/QPP pensionable earnings
• Box 24 — EI insurable earnings
• Box 29 — Employment code (if applicable)
• Box 40 — Other taxable allowances and benefits (car allowances, gifts)
• Box 50 — RPP or DPSP registration number (if employer has a plan)

Filing Deadlines and Methods

The T4 filing deadline is the last day of February each year. For 2025 tax year, T4 slips must be filed with CRA and distributed to employees by February 28, 2026.

• Deadline: last day of February (for the prior calendar year)
• Electronic filing required if filing 6 or more slips (as of 2024)
• Paper filing allowed only for 5 or fewer slips
• File via CRA My Business Account, web forms, or payroll software XML upload

The T4 Summary: What It Is and How to File

In addition to individual T4 slips, you must file a T4 Summary that totals all the amounts from your individual slips. This allows the CRA to reconcile your remittances against the total deductions reported.

The T4 Summary is filed at the same time as the individual slips through the same electronic or paper method.

• Totals from all T4 slips are carried to the corresponding summary boxes
• Box 82 — total CPP deducted
• Box 84 — total EI premiums deducted
• Box 86 — total income tax deducted
• Box 88 — number of T4 slips filed

Most Common T4 Errors and How to Avoid Them

These are the errors we most commonly correct when reviewing T4s prepared by Ontario small business owners.

• Missing employee SIN (never file without it — triggers CRA penalty)
• Incorrect employment income (missing bonuses, vacation payouts, taxable benefits)
• Wrong CPP and EI amounts (must match actual payroll records exactly)
• Forgetting to issue T4A for sub-contractors paid over $500
• Not filing T4s for terminated employees (still required)
• Mismatch between T4 summary totals and individual slips

Key Takeaways

T4 preparation is a detail-intensive annual obligation that rewards careful year-round payroll record-keeping. The more accurate your payroll throughout the year, the faster and simpler T4 season becomes. Consider outsourcing payroll entirely to a CPA to eliminate T4 errors and late filings.