How to Correct a Mistake on Your Canadian Tax Return

Finding an error after you file is stressful, but it is common and fixable. You can correct a mistake on your tax return by asking the Canada Revenue Agency (CRA) to reassess it. This guide explains which method to use, how long it takes, and what happens if you owe more tax. 

Can you fix a mistake on your tax return after you file it? 

Yes, you can. Do not file a second return for the same year. Instead, you send the CRA a change request. 

You need to wait for your notice of assessment before you change a return, whether you filed online or on paper. A request sent earlier cannot be processed. Your notice of assessment also shows what the CRA accepted, so read it first. The canada revenue agency may have already adjusted the item. 

What kinds of mistakes can you correct? 

Most errors fall into a few groups. The table below shows common examples and what each one usually changes. 

Corrections that help you and corrections that cost you follow the same process. Both should be fixed. 

How do you correct a mistake on your Canadian tax return? 

You have three options to amend your tax return. The first two are online. The third is by mail. 

The CRA calls online requests the faster option and mailed requests the slower option. The table compares them. 

The CRA lists about two weeks for online requests and about eight weeks for mailed requests. Peak filing season can add time. You can follow your request through the progress tracker in your CRA account. 

Online tools have limits. Refile cannot change returns before the 2021 tax year, bankruptcy returns, or optional returns for a deceased taxpayer. It also cannot change an unassessed return, or one the CRA has already reassessed nine times. You also cannot use it for personal details such as your address or direct deposit. Use your CRA account for those. 

What are the steps for a T1 adjustment request? 

The steps below work for all three methods. Only the way you send the request changes. 

1. Wait for your notice of assessment. 
2. Gather the slip, receipt or record that supports the change. 
3. List each line that changes, with the old and new amount. 
4. Check related lines, such as provincial tax and credits. 
5. Submit through Change my return, ReFILE, or mail. 
6. Save your confirmation and keep your records. 

For mailed requests, send the completed Form T1-ADJ and all supporting documents to your tax centre. Send it separately from your current year return. Keep your records for six years after the tax year. 

How far back can you amend your tax return? 

For individuals, you can generally request a change for the 10 most recent tax years. The CRA gives you 10 years from the original notice of assessment when an error works against you. Confirm the exact years on canada.ca, because online tools may show fewer. 

The limit is different for the CRA. It can reassess within set periods and for longer in cases of misrepresentation. If you owe tax from an old year, correct it as soon as you find it. 

What happens if the correction means you owe more tax? 

You will receive a notice of reassessment with the new balance. Interest applies, and in some cases so do penalties. 

The CRA charges interest from the original filing deadline, not from the date you ask for the change. The prescribed rate is set quarterly, so check the current rate on canada.ca. Penalties depend on the facts. A simple data entry error is treated differently from knowingly leaving income. 

Pay the balance as soon as you can. Interest keeps growing until you do. 

When should you use the Voluntary Disclosures Program? 

Use the Voluntary Disclosures Program (VDP) for larger or older problems, such as unreported income over several years. A regular change request suits a missed slip or a forgotten credit. 

For applications received on or after October 1, 2025, the CRA treats unprompted applications as eligible for 75% interest relief and 100% penalty relief. Prompted applications can receive up to 100% penalty relief but only 25% interest relief. Applicants now use Form RC199. 

Older articles still describe a General Program and a Limited Program. Those labels no longer apply. Speak with a tax professional before you apply. 

Does the process change by province or business structure? 

Yes. The basic steps above apply to personal T1 returns, but some situations differ. 

• Quebec: You file a separate provincial return with Revenu Québec. A change to your federal return may need a matching change there. 

• Other provinces and territories: The CRA handles provincial tax on your T1, so one request covers both. 

• Self-employed individuals: Business income and expenses sit on your T1. Update every connected line. 

• Corporations: A T2 return follows a separate reassessment process. Ask your accountant. 

• GST/HST: These returns have their own adjustment tools. A T1 change does not fix them. 

Changes to a corporation can also affect the owner’s personal return. Review both together. 

What if you disagree with the CRA’s decision? 

An adjustment request and a notice of objection solve different problems. Use an adjustment request when you made an error. Use an objection when you believe the CRA assessed you incorrectly. 

The objection deadline for an income tax reassessment is the later of one year after the filing deadline or 90 days from the notice. Mark the date on your notice as soon as it arrives. 

Frequently asked questions 

Can I correct my return before I receive my notice of assessment?

No. The CRA cannot process the change until the return has been assessed. 

Do I need an accountant to amend my tax return?

No, but one helps with business income, multiple years or larger balances. 

Will the CRA penalize me for fixing my own mistake?

Penalties depend on the facts. Correcting an honest error early is usually better than waiting. 

Which method is the fastest? Changing my return and Refile are the fastest options. 

Conclusion 

You can correct a mistake on your tax return with a clear process. Wait for your notice of assessment, gather support, and choose the online or mail method that fits. Review related lines and pay promptly if you owe more. 

For larger or older errors, the VDP may reduce your penalties and interest. An experienced accountant can also manage the request for you. This article is general information, so rules may vary by tax year and your situation.