Have you ever filed your tax return and then immediately realized something was wrong? Maybe you forgot a slip, entered the wrong amount, missed a deduction, or claimed a credit incorrectly. The good news is that mistakes on a Canadian tax return can often be corrected.
The most important thing is to avoid filing a second return for the same tax year. If you need to make a correction after filing, wait until the Canada Revenue Agency has assessed your original return and issued your Notice of Assessment. After that, you can request a change.
Here’s what to do if you make a mistake on your tax return in Canada.
Wait for Your Notice of Assessment
After you file your personal income tax return, the CRA will review it and issue a Notice of Assessment. This notice confirms the CRA’s initial assessment of your return, including whether you have a refund, a balance owing, or no amount owing.
You should wait until you receive your Notice of Assessment before requesting changes to your return. CRA guidance says not to file another return for the same year. Instead, after your return has been assessed, you can request a change using the CRA’s adjustment process.
Do Not File a Second Tax Return
If you notice an error after filing, do not submit another return for the same tax year. Filing a second return can create confusion and may delay processing.
Depending on the type of mistake, the CRA may correct certain slip-matching errors automatically. However, you should not assume this will happen. If the error affects your income, deductions, credits, benefits, or balance owing, review the proper adjustment options.
How to Change Your Personal Tax Return
Once your return has been assessed, you can request a change to your personal income tax and benefit return, also known as a T1 return.
There are three common ways to request a change.
1. Use Change My Return in Your CRA Account
The fastest option is often Change My Return through your CRA account. CRA says you can use this service to request many changes online, although some returns and situations cannot be changed this way, such as certain bankruptcy returns, optional T1 returns for deceased taxpayers, older returns, returns filed with the wrong province or territory of residence, and certain international or non-resident returns.
2. Use ReFILE Through Certified Tax Software
If you filed using certified tax software, you may be able to use ReFILE to make changes electronically. For the 2026 filing season, CRA says ReFILE can be used to file amended T1 returns for the 2022, 2023, 2024, and 2025 tax years.
Professional tax preparers may also be able to submit adjustments through ReFILE, depending on the software, authorization, and tax year.
3. Send a T1 Adjustment Request by Mail
If you cannot make the change online, you can request the change by mail. This is usually done by filing Form T1-ADJ, T1 Adjustment Request, or by sending a signed letter to your tax centre explaining the changes.
If you submit a request by mail, include the details of the change, the tax year involved, your social insurance number, address, phone number, and supporting documents for the change. Do not send original receipts unless the CRA asks for them.
How Far Back Can You Change a Return?
The CRA allows taxpayers to request changes to previous tax returns, but there are limits.
Generally, a change request made in 2026 must relate to a tax year after 2015 to be considered, and a refund cannot be issued for an adjustment request made more than 10 calendar years after the end of the tax year.
Some older or special returns may also have to be changed by mail rather than online.
What Happens After You Request a Change?
After you submit an adjustment request, the CRA will review it and either issue a Notice of Reassessment or send a letter explaining its decision.
For routine T1 adjustment requests, CRA’s 2025–2026 service standards say the goal is to issue a Notice of Reassessment or letter of explanation within two weeks for digital requests and within eight weeks for paper or telephone requests. Complex requests may take longer, and CRA’s service standard for complex T1 adjustment requests is 20 weeks.
CRA’s processing-times page also notes that T1 adjustment requests may experience delays due to higher-than-normal intake, and that complex requests can take longer when more information or additional verification is required.
What If the Mistake Means You Owe More Tax?
If your correction increases your tax owing, it is usually better to fix the issue as soon as possible. Interest may apply to unpaid amounts, and penalties may apply in some situations, especially if income was omitted or the error was significant.
If the mistake is serious, intentional, repeated, or involves unreported income from a prior year, speak with a qualified tax professional before submitting the change. In some cases, the Voluntary Disclosures Program may be relevant. CRA says the VDP may grant relief on a case-by-case basis to taxpayers and registrants who come forward to correct errors or omissions in their tax affairs, provided the program’s conditions are met.
What If the CRA Rejects the Change?
If the CRA does not accept your adjustment request, it will send a letter explaining why. Review the explanation carefully. You may need to provide additional documents, correct the request, or consider whether a formal objection is appropriate.
A tax adjustment request is different from a Notice of Objection. If you disagree with an assessment or reassessment, there are specific objection deadlines and procedures. Speak with a tax professional if the issue involves a larger balance, denied credits, business income, shareholder benefits, GST/HST, payroll, or potential penalties.
Common Mistakes You May Need to Correct
Common tax return mistakes include:
- forgetting a T4, T5, T3, T4A, T4E, T4RSP, T4RIF, or other slip;
- entering income, deductions, or credits incorrectly;
- forgetting to report self-employment, rental, investment, foreign, or capital gains income;
- claiming a deduction or credit you were not eligible for;
- forgetting eligible medical expenses, tuition amounts, donations, RRSP contributions, or childcare expenses;
- using the wrong province or territory of residence;
- missing foreign reporting requirements; or
- entering incorrect marital status, dependant, or benefit-related information.
Some of these can be simple adjustments. Others may affect benefits, credits, interest, penalties, or future CRA reviews.
Speak with a Professional
If you make a mistake on your tax return, do not panic. Many errors can be corrected through CRA’s adjustment process after your return has been assessed. The key is to use the correct method, include proper supporting documents, and act promptly if the mistake affects your balance owing.
If you are unsure how to correct a return, if the mistake involves business income, rental income, foreign income, shareholder transactions, GST/HST, payroll, or a large balance owing, speak with an experienced accountant before submitting the adjustment.
If you need help correcting a tax return or responding to the CRA, contact us for guidance. Our team can review your situation, help prepare the adjustment request, and advise you on the best next steps.
E&E Professional Accountants has years of experience in assisting businesses with their accounting needs. We are founded and managed by an experienced corporate auditor and a former CRA tax auditor. Feel free to contact us for assistance with all your accounting and bookkeeping needs.