Fixing T4 mistakes might not be on your radar until it suddenly is. You’ve filed your slips, submitted your T4 Summary, and then realize something’s off. Maybe the income was entered wrong, a taxable benefit was missed, or worse, you forgot an employee entirely.
If you’re thinking “I made a mistake on a T4… now what?”, take a breath. You’re not alone, and the good news is that the CRA has a process for this. The key is to act quickly and file the correction properly.
In this post, we’ll walk you through how to fix a T4 after filing, the most common T4 mistakes, and how to submit an amended T4 slip to stay on the CRA’s good side.
Common T4 Mistakes to Watch Out For
Even when you’re using payroll software or working with a bookkeeper, mistakes can happen, and the CRA sees a lot of the same ones every year. Here are the most common errors we see:
- Reporting the wrong amount of employment income
- Forgetting to include taxable benefits in Box 40
- Missing an employee who received income during the year
- Entering amounts into the wrong boxes (like putting bonuses under non-taxable codes)
- Filing the wrong year or employer account number
These may seem small, but they can result in employees receiving incorrect tax slips or trigger a penalty for incorrect T4 if the CRA catches it before you do.
Sometimes, new things show up on T4s or other tax slips. For example, CPP2. Read more about it in CPP2 Checklist for 2025: What Every Small Business Owner Needs to Know (and How It Affects How You Pay Yourself).
How to Correct a T4 After It’s Been Filed
So, how do you fix a T4 after filing?
First, confirm the exact nature of the mistake. Was it a dollar amount, a missing box, or a missing slip altogether? Once you’ve identified the issue, the solution depends on how you originally filed.
If you filed electronically using payroll software:
- Go back into your payroll or tax filing software
- Select the employee’s T4 slip and update the incorrect information
- Mark the slip as “Amended”
- Resubmit it to the CRA electronically
- Make any corresponding changes to the T4 Summary
If you filed by paper:
- Download a new T4 slip
- Fill it out with the corrected information
- Mark the top right corner of the slip as “AMENDED”
- Complete a new T4 Summary if needed
- Mail the corrected forms to the CRA
Make sure your amended T4 slip matches the correction exactly and avoid changing anything else unless necessary.
How to Resubmit an Amended T4 Slip to the CRA
Resubmitting a corrected T4 is simple, but it must be done the right way to avoid confusion or duplicate records.
Here’s what to remember:
- Use the same T4 format you originally used, whether electronic or paper
- Clearly mark the corrected slip as “Amended”
- Update your payroll or accounting records to reflect the correction
- If your mistake affects remittances, adjust those as well
The CRA’s systems are automated and will look for consistency. An amended T4 needs to line up with your T4 Summary and any remittances you’ve made throughout the year.
Speaking of throughout the year, that’s when you should be thinking about your small business taxes. Read Tax Planning Isn’t Just for April — It’s for Ambition to learn why.
Will You Be Penalized? Understanding CRA’s Process and Deadlines
Now for the question most business owners ask: Will I be penalized for an incorrect T4?
The answer is that it depends.
If your error caused an employee to underreport income or led to incorrect deductions, the CRA may apply penalties or interest. But if you catch the mistake early and correct it proactively, penalties are often reduced or avoided altogether.
Timing matters. The longer you wait to fix a T4 mistake, the more likely the CRA is to impose a penalty for incorrect T4 filing, especially if it affects tax withholding or benefits.
What happens if the CRA audits you? Take a look at Could You Keep a Straight Face to a CRA Auditor?
What to Gather Before Contacting the CRA
Before you submit an amended slip or call the CRA, it’s a good idea to get organized. Here’s what to collect:
- Original T4 slip as filed
- Payroll reports and year-to-date summaries
- Remittance records
- Source documentation such as bonus approvals or benefit calculations
- A brief written explanation of the correction
This information can help you answer CRA questions quickly if they follow up on your amendment and it shows you’re taking steps to stay compliant.
Final Thoughts: Fix the Error, Protect Your Business
Mistakes happen. What matters is how quickly and accurately you correct them.
Whether it’s a small typo or a bigger issue like a missing employee, fixing T4 mistakes the right way helps protect your business and keeps your team’s records accurate.
If you’ve found an error and aren’t sure how to handle the correction, we can help. At Swain CPA, we work with business owners across Canada to make sure T4s and year-end compliance are done right.
Contact us today for support with T4 amendments or reviews.
FAQ: Fixing T4 Mistakes and CRA Corrections
1. I made a mistake on a T4. What should I do?
File an amended T4 slip as soon as possible. Correct the error in your software or manually on paper, and ensure the correction is clearly marked.
2. How do I fix a T4 after filing?
If you contact your CPA with the correct T4, they can update it for you. Alternatively, log into your payroll software and update the T4 slip, marking it as “Amended.” If filing by paper, reprint the slip, correct the error, and write “AMENDED” at the top. You may also need to update your T4 Summary.
3. What are the most common T4 mistakes?
Some common T4 mistakes include incorrect income amounts, missing employees, forgotten taxable benefits, or using the wrong T4 boxes.
4. Will I face a penalty for incorrect T4 information?
The CRA may apply a penalty for incorrect T4 slips, particularly if the mistake results in underreported income. Fixing the error early reduces the likelihood of penalties.
5. What documents should I prepare before resubmitting a corrected T4?
Gather your original T4, payroll records, supporting documents such as benefit calculations or bonuses, and a short note explaining the correction. Being organized can speed up the correction process and limit CRA follow-up.
