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If your accountant makes a mistake in Canada, the tax is still yours to fix. The CRA says you’re generally responsible for errors made by your representative or another third party. So work out what went wrong, correct the return, then ask for penalties and interest to be cancelled if you have a real case.
Taxpayers are generally considered responsible for errors made or delays caused by third parties acting for the taxpayers for income tax matters.
Taxpayer Relief Provisions (IC07-1R1), canada.ca
First, find out exactly what’s wrong
Get the details in writing. Which return, which year, which line, and what the right figure is? Ask the accountant for the working papers behind the number. A vague “there was a small error” won’t help you when the CRA writes back.
Then check whether it costs you or saves you. A missed expense means you overpaid. An omitted slip means you underpaid, and the CRA will charge interest on the gap. The direction decides how urgent it is.
How do you correct a personal return?
Once you have your notice of assessment, you can change a T1 online with “Change my return” in your CRA account, or through your tax software’s ReFILE service. The CRA says online changes take about two weeks. You can also mail form T1-ADJ with supporting documents, and that takes about 20 weeks. The CRA answers with a notice of reassessment if it approves the changes, in whole or in part. Requests that cover several years or years beyond the normal reassessment period can take up to 36 weeks. The steps are on the CRA’s page on changing your return.
Refunds have a limit. The CRA won’t issue refunds for adjustments requested more than 10 calendar years after the end of the tax year, as its page says for older returns. Don’t sit on it.
We didn’t verify the steps for corporation returns or GST/HST filings, so for those, ask the accountant to send the correction through the right channel and keep proof.
What does an error cost?
Say your accountant left $10,000 of business income off your return. You’re an Ontario sole proprietor who really earned $80,000, and the return showed $70,000. The self-employed tax calculator gives $13,233.57 of income tax at $80,000 and $10,384.82 at $70,000. That’s $2,848.75 of extra income tax. CPP on both halves goes from $7,913.50 to $8,892.90, another $979.40.
That tax was always yours to pay. What the mistake adds is interest, which the CRA charges compounded daily from the day after the due date, and possibly a penalty. The longer you wait, the bigger that part gets.
Can you get penalties and interest cancelled?
You can ask, using form RC4288. The CRA lists extraordinary circumstances, financial hardship, and its own errors or delays as grounds. On representatives, it says relief may be granted in exceptional situations. So don’t assume that “my accountant did it” is enough by itself. It isn’t.
A request only covers tax years or periods ending in the last 10 calendar years. Interest counts only if it accrued in that window. Include dates, names and any written advice you were given.
If the mistake is old, the Voluntary Disclosures Program handles errors and omissions. Since October 1, 2025 it also accepts some applications made after the CRA has sent a letter about a possible problem, though not from people under audit or investigation. Relief can cover penalties and part of the interest, depending on the type of application, and you still pay the tax.
What about the accountant?
Talk to them first. Ask for a fix, and ask who covers any penalties and interest that result. Many firms carry insurance for this, but we couldn’t confirm the specifics for any firm or professional body, so ask directly. If they refuse, look up whether they belong to a professional body and how it handles complaints. Keep every email.
Before your next filing, read what’s being submitted. Compare your own numbers, using the take-home pay calculator for employment income or the corporate tax calculator for a company. If the totals are far apart, ask why before signing.
What does a sensible order of steps look like?
Picture Neil in Regina, who finds out in October that his 2024 return missed a T5 slip. First he gets the accountant to confirm the error in an email. Then he checks his notice of assessment and files the change online. Next he pays the extra tax right away, so interest stops growing. Last, he decides whether a relief request is worth it, and if so he fills in RC4288 and attaches the emails. Doing the money step first matters, because interest keeps running until the tax is paid.
Mistakes people make after an error
Staying silent is the big one. Interest doesn’t wait. Others: paying the accountant’s invoice while ignoring the CRA letter, or sending a correction with no support. Missing the reply date on a CRA letter matters too.
Where this information comes from
The change-a-return steps and time limits come from the Canada Revenue Agency‘s page on changing a T1 return. Relief and disclosure rules come from its taxpayer relief and Voluntary Disclosures Program pages. The tax figures come from this site’s calculator, which uses 2026 rates and leaves out EI, GST/HST and business expenses. We checked these CRA pages in November 2026. This site isn’t connected to the CRA or any government.
Frequently asked questions
Am I responsible if my accountant makes a mistake?
Generally yes. The CRA's taxpayer relief circular says taxpayers are generally responsible for errors made or delays caused by third parties acting for them. Relief for an accountant's error is possible only in exceptional situations, so do not count on it. Fix the return first, then decide whether to ask for relief.
How do I correct a filed personal return?
Once you have your notice of assessment, use Change my return in your CRA account or ReFILE in certified tax software. Online changes take about two weeks. You can also mail form T1-ADJ with support, which takes about 20 weeks. The CRA replies with a notice of reassessment showing what it changed.
How far back can I ask for a refund or penalty relief?
The CRA will not issue refunds for adjustments requested more than 10 calendar years after the end of the tax year. Taxpayer relief requests also cover only tax years or periods that ended in the last 10 calendar years, and interest only if it built up in that window. Do not wait.
How do I ask to have penalties and interest cancelled?
Use form RC4288 or apply online through your CRA account. Give dates, the tax years involved, what went wrong and any written advice from the accountant. The CRA looks at extraordinary circumstances, financial hardship and its own errors or delays. Relief is discretionary, so you may still owe the money.
Can I recover the cost from the accountant?
Ask the accountant to fix the error and to say who covers resulting penalties and interest. Many firms carry insurance, but we could not confirm details for any firm. If they refuse, check which professional body they belong to and how it handles complaints. Keep every email and working paper.
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