Home » The Amended Return: What to Do When You Discover You Filed Wrong
Portal Login
Toll free 855 667 1727
100% accuracy guaranteed
The Amended Return: What to Do When You Discover You Filed Wrong
You filed your tax return a while ago. Then you're reviewing your records and you realize: I made a mistake.
Missed a deduction. Forgot to report income. Claimed something that doesn’t qualify. Made a calculation error.
The return is already filed. CRA processed it. You received your Notice of Assessment.
Now what?
Most Ontario business owners facing this situation fall into one of two camps:
They panic and do nothing, hoping CRA won’t notice the error.
Or they assume fixing it is complicated, expensive, and will trigger an audit.
Neither assumption is quite right.
At KKCPA, we see business owners discover filing errors regularly. Some errors are minor and inconsequential. Others are significant and costly if not corrected. Understanding when you need to file an amended return, how the process works, and what happens when you correct errors voluntarily versus when CRA catches them—that determines whether a mistake becomes a manageable correction or a serious problem.
Here’s what Ontario business owners need to know about amended returns and why how you handle discovered errors matters.
What an Amended Return Actually Is
When you file your tax return and later discover an error, you can’t just file a new return. That’s not how the system works.
For individuals (T1 returns):
You file a T1 Adjustment request (T1-ADJ). This is a form that tells CRA what needs to change on your already-filed return.
For corporations (T2 returns):
You file an amended T2 return showing the corrections.
The distinction from original filing:
An amended return references your original filed return and specifies what’s changing. It’s not starting from scratch—it’s correcting specific items.
What you can amend:
Income you forgot to report or incorrectly reported. Deductions or credits you missed claiming. Amounts you claimed incorrectly. Information that was wrong (dependents, business income classification, etc.).
What you generally can’t amend (or shouldn’t try):
Fundamental changes to your filing status or business structure that would require different forms entirely. Things that would require re-characterizing the nature of transactions rather than correcting amounts.
The timing:
For most adjustments, you have up to 10 years from the end of the tax year to request changes. But waiting years to correct known errors creates other problems.
The Voluntary Correction Advantage
There’s a significant difference between you discovering an error and correcting it versus CRA discovering the error during a review or audit.
When you correct voluntarily:
CRA generally waives penalties (though you still owe any additional tax plus interest from the original due date).
The correction is straightforward. You explain what was wrong, provide supporting documentation, CRA adjusts.
It demonstrates good faith. You’re not trying to hide anything—you found a mistake and fixed it.
When CRA discovers the error:
They assess penalties on top of the additional tax and interest.
They scrutinize other aspects of your return more closely. If you made one error, what else is wrong?
It creates credibility concerns that follow you in future years. CRA flags your file for closer examination.
The penalty difference:
Gross negligence penalties can be 50% of the additional tax owing. For substantial errors, that’s significant money.
If CRA determines you knowingly filed incorrect information, penalties escalate further.
The calculation:
You discover you forgot to report $20,000 in income. You owe approximately $8,000 in additional tax (depending on your bracket).
If you correct voluntarily: You owe $8,000 plus interest from the original due date. No penalties.
If CRA discovers it during audit: You owe $8,000 plus interest PLUS potentially $4,000 in penalties (50% of the tax).
That’s a $4,000 difference just for being proactive about fixing your own mistake.
When You Should File an Amended Return (And When You Shouldn’t)
Not every discovered error requires an amended return.
You should file an amended return when:
The error affects your tax owing (you owe more or are owed a refund). The error involves reporting requirements (missed income reporting, incorrect classifications). The error could trigger penalties if discovered by CRA. The error affects benefits or credits tied to your return.
You might not need to amend when:
The error is truly immaterial (changes tax owing by trivial amounts). Correcting it would cost more in professional fees than the tax impact. The error is in your favor and correcting it would increase what you owe (though this creates ethical and legal considerations).
The gray area:
You claimed a deduction you’re not entitled to, but CRA hasn’t questioned it. Do you voluntarily give up the deduction?
Legally, you should correct it. Practically, many business owners struggle with voluntarily increasing their tax bill.
This is where understanding the consequences of different approaches matters. The cost of correcting now versus the cost if CRA discovers it later (penalties, interest, scrutiny) might make voluntary correction the better financial choice even though it feels counterintuitive.
The Types of Errors That Matter Most
Some filing errors are more consequential than others.
High-risk errors CRA cares about:
Unreported income: You forgot to include T4s, T5s, self-employment income, or other taxable amounts. CRA receives copies of information slips. They know what income was reported to you. If it’s missing from your return, their systems flag it.
Overstated deductions: You claimed expenses that don’t qualify, or claimed amounts higher than what you can support.
Incorrect business vs. personal classification: You claimed personal expenses as business expenses. You classified income incorrectly to access more favorable tax treatment.
Errors in credits or benefits: You claimed credits you don’t qualify for. You reported information that affects benefit calculations incorrectly.
Low-risk errors (from CRA’s perspective):
Math errors that don’t materially change your tax owing. Minor classification differences that don’t affect the outcome. Errors in information that doesn’t impact your tax calculation.
Why the distinction matters:
High-risk errors should be corrected immediately once discovered. The longer you wait, the worse it looks if CRA finds it first.
Low-risk errors might not warrant the cost of amending, depending on the impact.
The Timeline That Shapes Your Options
When you discover an error affects what you should do about it.
You discover the error before CRA processes your return:
Best case scenario. You can often submit corrections before they finalize assessment. This is treated almost like filing correctly the first time.
You discover the error shortly after filing (weeks or a few months):
Still good timing. Amending is straightforward. It’s clear you discovered the error through your own review, not because CRA asked questions.
You discover the error months or years later:
More complicated. CRA may question why it took so long to discover. If they’ve already reviewed your return and accepted it, re-opening it creates scrutiny.
You discover the error after receiving a CRA information request:
Timing looks suspicious. CRA asked about something, you “suddenly discovered” an error. They may view this as a response to getting caught rather than genuine discovery.
This is why the voluntary disclosure program exists—for situations where you’re correcting before CRA finds it, but the timing is less than ideal.
What Actually Happens When You File an Amended Return
You submit your T1-ADJ or amended T2. Then what?
CRA’s review process:
They examine what you’re changing and why. They may request supporting documentation for the corrections. They assess whether the changes are legitimate.
Possible outcomes:
They accept the changes and reassess your return. You receive a revised Notice of Assessment showing the corrections.
They partially accept the changes. Some corrections go through, others don’t.
They deny the changes. Your original assessment stands.
The timeline:
Simple amendments might process in weeks. Complex amendments or those requiring significant documentation review can take months.
During this time, if the amendment increases your tax owing, you owe that amount plus interest. The clock started ticking from your original filing due date, not from when you filed the amendment.
What triggers scrutiny:
Multiple amendments to the same return. Amendments that dramatically change your originally filed amounts. Amendments claimed years after the original filing. Amendments that seem to conveniently align with CRA’s areas of focus in audits.
The Voluntary Disclosure Program: When Simple Amendment Isn’t Enough
For some situations, filing a regular amended return isn’t appropriate. The error is substantial, the timing is problematic, or the circumstances suggest something beyond simple mistake.
When Voluntary Disclosure Program (VDP) applies:
You failed to report significant income over multiple years. You claimed ineligible deductions repeatedly. You have offshore income or assets you didn’t report. The error could be interpreted as intentional evasion rather than innocent mistake.
What VDP offers:
Relief from prosecution. Waiver of penalties (in most cases). Relief from some interest charges (in limited circumstances). A way to correct serious errors without facing the full consequences of CRA discovering them.
The requirements:
You must disclose before CRA initiates any action against you (audit, investigation, etc.). The disclosure must be complete (all years, all issues). You must be cooperative and provide all requested information.
Why this matters for business owners:
If you discover an error that spans multiple years or involves substantial amounts, determining whether it’s an amendment situation or a VDP situation requires understanding the program requirements and CRA’s enforcement priorities.
Getting this wrong—filing a simple amendment when you should have gone through VDP, or vice versa—can eliminate options and protections you would otherwise have.
The Cost of Waiting to Correct Known Errors
You discover an error. You know you should fix it. But you wait.
Why business owners delay:
“I’ll deal with it next year when I file.” “Maybe CRA won’t notice.” “I don’t want to pay the additional tax right now.” “I’m hoping the situation will somehow resolve itself.”
What happens during the delay:
Interest accrues daily on any additional tax owing. If CRA discovers the error before you correct it, you lose the voluntary correction advantage. The longer you wait, the less credible your claim that you “just discovered” the error. Your stress increases knowing there’s an unresolved tax problem.
The cost comparison:
You discover in May that you owe an additional $5,000. You amend immediately: You owe $5,000 plus two months of interest (roughly $40).
You wait a year to amend: You owe $5,000 plus 14 months of interest (roughly $280).
CRA discovers it during audit two years later: You owe $5,000 plus 26 months of interest (roughly $520) PLUS penalties (potentially $2,500).
Waiting turned a $5,040 problem into an $8,020 problem.
When “I’ll Just Wait and See” Becomes a Problem
Some business owners, discovering they made an error in CRA’s favor (claimed less than entitled, reported more income than required), adopt a “wait and see” approach.
“If CRA asks about it, I’ll explain. Otherwise, I’ll just leave it.”
Why this seems logical:
You’re not hiding anything—the information on your return is verifiable. CRA could theoretically see the error themselves and correct it. You’re not obligated to maximize your tax benefit.
The problems this creates:
CRA generally doesn’t review returns looking for ways to give you more money back. If you missed a deduction, they’re unlikely to tell you.
If they do review your return and make corrections in your favor, they may scrutinize other areas more closely. “If they missed this obvious deduction, what else is wrong?”
If you later need to amend for other reasons, having uncorrected known errors on file creates inconsistency concerns.
The better approach:
If you discover errors—whether in your favor or CRA’s—correct them. It demonstrates diligence and accuracy, which matters in future dealings with CRA.
What You Can’t Fix With an Amended Return
Some “errors” aren’t correctable through simple amendment.
Fundamental strategy changes:
You filed as self-employed but wish you’d incorporated. You took salary but wish you’d taken dividends. You claimed CCA but wish you hadn’t.
These aren’t errors—these are choices you made that you now regret. CRA doesn’t allow retroactive do-overs of strategic decisions.
Elections and designations:
Many tax elections have strict deadlines. If you failed to make an election when filing, you often can’t add it through amendment.
Structural changes:
Changing the fundamental characterization of transactions, relationships, or arrangements usually requires more than amendment—and may not be possible at all.
Why this matters:
Understanding the difference between “I made an error in reporting what happened” and “I wish I’d structured things differently” is critical.
Errors are correctable. Regretted strategic choices usually aren’t.
The Professional Fees Question
Filing an amended return isn’t free. If you use a tax professional to prepare and file amendments, there are fees.
The calculation business owners make:
“The error only affects my tax by $200. The accounting fee to amend will be $300. Why would I pay $300 to fix a $200 problem?”
Why this calculation is incomplete:
The $200 is the current tax impact. If CRA discovers the error later, penalties could be 50% of the tax ($100) plus you’ll pay professional fees to deal with the audit anyway.
Some errors, if left uncorrected, create larger problems in future years or trigger scrutiny of other areas.
The peace of mind of knowing your returns are correct has value beyond the immediate dollar calculation.
When the math works against amending:
Truly trivial errors with no penalties at risk and minimal future impact. Errors where the cost of correction genuinely exceeds any plausible downside. Old tax years where the 10-year window is about to close and the likelihood of CRA review is extremely low.
The judgment call:
This isn’t a simple “always amend” or “never amend trivial errors” answer. It depends on the specific error, the amounts involved, the risk profile, and your relationship with CRA historically.
Making this assessment requires understanding CRA’s enforcement priorities and penalty structures—not just comparing the current tax difference to the amendment fee.
The Multiple Error Problem
You discover one error. You start reviewing more carefully. You find another error. And another.
The question becomes:
Do you amend for each error separately? Wait and amend for all of them at once? Fix some and not others?
The considerations:
Multiple amendments to the same return create scrutiny. CRA starts wondering how many errors are actually there and whether your returns are reliable.
Waiting to batch amendments might mean some errors remain uncorrected for extended periods, accruing interest.
Fixing some errors but not others creates inconsistency if CRA reviews and discovers the uncorrected errors.
The better approach:
If you’re discovering multiple errors, conduct a comprehensive review of the return before amending anything. Correct everything that needs correcting in one amendment rather than piecemeal corrections.
This requires professional review to ensure you’ve actually identified all the problems before filing corrections.
What CRA Thinks About Serial Amendments
One amendment: You found an error and fixed it. Reasonable.
Multiple amendments to the same return: CRA starts questioning the quality of your original filing and whether there are more errors you haven’t found yet.
Amendments to multiple years: Pattern concerns. Were these isolated errors or systematic problems with how you prepare returns?
The credibility issue:
Each amendment uses up a bit of goodwill with CRA. You’re asking them to reprocess your return, review documentation, issue a new assessment.
If this happens repeatedly, they start treating your returns with more skepticism and scrutiny going forward.
The flag in the system:
CRA’s systems track amendments. Multiple amendments, especially if they’re always in your favor (claiming more deductions, reporting less income), create a pattern that makes you a higher audit risk in future years.
The takeaway:
Get it right the first time. If you can’t get it completely right, do thorough review before amending so you fix everything at once rather than discovering errors in waves.
The Bottom Line
Tax return errors happen. Documents get overlooked. Deductions get missed. Amounts get miscalculated.
When you discover errors after filing, you have options. Filing amended returns is a normal part of the tax system.
But how you handle corrections matters. Voluntary versus discovered by CRA. Immediate versus delayed. Comprehensive versus piecemeal.
Getting it right means understanding when errors are significant enough to warrant correction, how to correct them properly, and what consequences follow from different approaches.
Getting it wrong means paying unnecessary penalties, creating credibility problems with CRA, and turning simple mistakes into complex problems.
Need Help Determining Whether to Amend Your Return?
At KKCPA, we help Ontario business owners assess discovered errors and determine the appropriate correction approach.
We can help you:
- Review your return to identify all errors, not just the one you discovered
- Assess whether errors are significant enough to warrant amendment
- Determine if voluntary disclosure program applies to your situation
- Prepare and file amended returns or adjustment requests properly
- Calculate the cost of correcting now versus the risk of CRA discovering later
- Represent you with CRA during the amendment review process
Don’t let a discovered error become a bigger problem through inaction or incorrect correction approach.
📍 Serving Ontario businesses including Hamilton, Ancaster, Burlington, and the Greater Toronto Area
📞 Toll Free: 855-667-1727
Related Reading: