It is a common panic moment, but don't worry—people realize they made mistakes on their taxes all the time.
The short answer is no, there is no strict, immediate legal penalty just for discovering an honest mistake after the fact, provided you didn't knowingly try to mislead the Canada Revenue Agency (CRA) when you filed.
However, whether you should correct it depends heavily on what kind of mistake it is. Here is a breakdown of your obligations and exactly how to fix it.
1. Do You Owe Money or Are You Owed Money?
- If the mistake means you owe more tax: You aren't legally forced to immediately adjust it, but it is highly recommended that you do. If you leave it, the CRA will likely find it during their routine data-matching process. When they do, they will retroactively charge you the tax owed, plus compounded daily interest and potentially penalties.
- If the mistake means you missed a deduction/credit (You are owed money): You are completely free to leave it alone, but you'd be leaving your own money on the table. You have up to 10 years to go back and claim missed deductions.
2. The Golden Rule: Wait for Your NOA First
Do not try to refile or change your taxes right away. If you try to submit a correction while your tax return is still being processed, it will cause a massive logjam in the CRA system. You must wait until you receive your official Notice of Assessment (NOA). Once you have that document in hand or on your CRA portal, you can officially submit your fix.
3. How to Correct the Mistake if you filed your taxes yourself
Once you have your NOA, you do not file a brand new tax return from scratch. Instead, you file an adjustment. You can do this in three ways:
Option A: Use "ReFILE" (Fastest)
If you used certified tax software (like TurboTax, Wealthsimple Tax, H&R Block, etc.) to submit your return, log back into that software. Update the numbers to what they should be, and look for the ReFILE option. This electronically transmits just the corrected sections to the CRA.
- Processing time: ~2 weeks.
Option B: Use CRA "My Account"
Log into your CRA My Account portal. Navigate to the "Change My Return" service, select the correct tax year, find the specific line number that had the error, and type in the correct amount.
- Processing time: ~2 weeks.
Option C: By Mail (Paper)
If you prefer paper or have a complex adjustment that requires physical proof, fill out Form T1-ADJ (T1 Adjustment Request). Mail the completed form along with your supporting documents (like the missing slip or receipt) to your local tax centre.
- Processing time: ~8 weeks.
If we filed your taxes this year, we can easily refile on your behalf if you let our office know tht you failed to include something when you brought in your tax information.