I Forgot to Include a T4 Slip on My Tax Return: What Happens and How to Fix It

Leaving a T4 slip off your return is one of the most common filing errors. It happens most often when you had two jobs, left an employer mid-year, did seasonal or contract work, or misplaced a slip. (Employers file T4s; as an employee you report them.) The CRA already has a copy of every T4, so the question isn’t whether it will notice, but when, and the fix is straightforward. This page is part of the guide to filing a tax return in Canada.

Why the CRA already knows about your missing T4

Every employer must file T4 slips with the CRA by the last day of February after the tax year. The CRA’s systems match employer-reported T4 data against filed returns, and a return that’s missing T4 income gets flagged. This matching usually happens a few months after the filing deadline, so many people get a reassessment in late summer or fall.

What happens if the CRA finds it first

If you don’t correct the return yourself, the CRA issues a Notice of Reassessment that:

• Adds the missing income to your taxable income
• Recalculates your tax owing
• Charges arrears interest from the balance-due date (April 30) at the CRA prescribed rate, currently 7% a year, compounded daily
• May reduce a refund you already received or create a new balance owing

If the missing T4 made your refund too large, you’ll repay the difference plus interest. Correcting the return yourself before the CRA’s matching catches it is faster, and the guide to reading your Notice of Assessment explains the reassessment you’ll get either way.

If you haven’t filed yet

Include every T4 in the return: employment income goes on line 10100 and the income tax deducted on line 43700, for each slip.

If the filing deadline is close and a T4 still hasn’t arrived, you can file on time using your best estimate from your last pay stub, then correct the figures once the slip arrives. When you owe, filing late adds a late-filing penalty on top of interest, so an on-time return with a small error costs less than a late one.

How to fix a return you’ve already filed

Step 1: Find the missing T4

• CRA My Account. Under Tax information slips, select the tax year: every T4 your employers filed is listed, including ones you may have forgotten. The CRA My Account guide covers sign-in.
• The employer. Payroll can reissue a slip you’ve lost. If the employer has closed or can’t be reached, the CRA can help; its numbers are on the CRA contact information page.
• Your last pay stub. Box 14 (employment income) on the T4 matches the year-to-date earnings on your final stub of the year; how to read your pay stub explains the fields.

Step 2: Change the return

What to change for a missing T4:

• Line 10100: the corrected total employment income, including the missing slip
• Line 43700: the corrected total income tax deducted, adding Box 22 of the missing slip
• CPP and EI: add the slip’s CPP contributions (Box 16) and EI premiums (Box 18), so the return can credit them and work out any overpayment
• An explanation such as “Adding T4 from [employer name] not included in original filing”; a paper request includes a copy of the T4

You can submit the change online through My Account, through certified software, or on paper; the ways to change a filed return, and how long each takes, are on I made a mistake on my tax return.

Step 3: Pay any balance promptly

Once the CRA reassesses, paying the balance stops further interest. The ways to pay the CRA include My Account, online banking and Canada Post.

What you’ll likely owe

Adding a forgotten T4 almost always means more tax. The amount depends on:

• The employment income on the T4, taxed at your marginal rate
• CPP and EI: if your other employer didn’t reach the maximums, you may owe nothing extra; if both employers deducted independently, you may have over-contributed, and the excess CPP and EI is refunded when the return is reassessed
• Interest from the balance-due date on any additional tax

Two employers: why the second T4 often means a bill

Each employer withholds as if its job were your only income and applies the full basic personal amount (unless you told it otherwise on your TD1 form). With two jobs, too little tax is withheld overall, and adding the second T4 to the return brings the bill to the right level. This is one of the most common reasons for an unexpected balance; why do I owe taxes this year has a worked example and how to change withholding for next year.

What if your employer made the error?

If your employer left CPP contributions, EI premiums or income tax off the T4, or reported a wrong amount, ask the employer for an amended slip first. If it won’t correct it, the CRA can be contacted to resolve it. Employees are not penalized for an employer’s T4 errors once they are corrected.

More than one missing year

If you have several unfiled years or a pattern of unreported income that goes beyond a single slip, the Voluntary Disclosures Program lets you come forward and may waive penalties and some interest. Other slips left off a return have their own pages: unreported interest income, for example, covers a missing T5.