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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 the practical order is: work out what went wrong, correct the return, and then ask for penalties and interest to be cancelled if there’s a real case for it.
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 around 19 weeks. The CRA answers with a notice of reassessment if it approves the changes, in whole or in part.
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 you’d rather come forward before the CRA notices, the Voluntary Disclosures Program handles errors or omissions. It has to be voluntary, complete, involve a penalty, and cover information at least one year past due. It can give relief from prosecution and, sometimes, penalties, but you still pay the tax and interest.
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.
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 the numbers come 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.
Frequently asked questions
Am I responsible if my accountant made the error?
The CRA says you are generally responsible for errors made by your representative or another third party. Relief may be granted in exceptional situations.
How do I fix a mistake on my personal tax return?
After your notice of assessment, use Change my return in your CRA account or ReFILE in your tax software. You can also mail form T1-ADJ.
How far back can I ask for penalty relief?
The CRA considers penalties for years ending in the last 10 calendar years before the year of your request, and interest accrued in that same window.
Can I claim my accountant's fee back?
We couldn't confirm any rule on this. Talk to the accountant first and ask who covers penalties and interest caused by their error.
Should I tell the CRA before it finds the error?
The Voluntary Disclosures Program is for people who come forward first. It can relieve prosecution and sometimes penalties, but you still pay the tax and interest.
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Information only. This page is general information, not tax, legal or accounting advice. Tax-Services.ca is an independent publisher: we don't prepare or file tax returns or offer tax services, and we have no connection with the CRA, Revenu Québec, any government or any company named on this page. Check the figures that matter with an official source or a qualified professional.