How to Change a Canadian Tax Return After You Have Already Filed It

Do not file a second tax return for the same year

If you discover missing income, an unclaimed deduction, a forgotten tax slip or another error after submitting your Canadian personal tax return, the correct process is to request an adjustment to the assessed return.

The Canada Revenue Agency specifically says to wait until you receive your notice of assessment before requesting the correction. Sending another complete T1 return for the same tax year is not the normal way to fix an already filed and assessed return.

You can request changes for situations such as reporting income you missed, correcting an amount, claiming an eligible deduction, credit or expense, or adding a missing information slip or receipt.

What can you change after filing?

The CRA lists common adjustment situations that include:

• reporting income that was omitted, such as income from a T4 slip or tips;
• claiming or correcting a deduction, tax credit or expense, such as childcare or medical expenses;
• adding a missing tax document, such as an RRSP contribution receipt; and
• correcting figures entered on specific lines of an assessed T1 return.

The tax-return adjustment process is not the correct way to change every type of information. The CRA says Change my return cannot be used simply to update personal information such as your mailing or email address, direct-deposit information, marital status or name. It also cannot be used to make or revise certain elections or to allocate a refund to another CRA account.

Wait until the CRA assesses the original return

You must receive your notice of assessment, or NOA, before submitting an adjustment request. This allows the CRA to process the original return first and creates the assessed figures that your adjustment will change.

If you have already requested a change, the CRA also instructs you to wait until it responds before submitting additional changes to that same return. Sending overlapping requests can complicate processing.

Your three main options for changing a tax return

For an eligible T1 personal return, there are three principal ways to request a change:

1. Change my return in your CRA account;
2. ReFILE through certified tax software; or
3. Form T1-ADJ submitted by mail.

Online adjustment requests are generally faster. The best method depends on the tax year, how the original return was filed and whether any CRA restrictions apply to your situation.

Option 1: Change my return in your CRA account

For most ordinary individual tax situations, Change my return is the simplest way to correct an assessed return.

The CRA's current instructions are:

1. Sign in to your CRA account.
2. Select Individual if you are changing your own return.
3. Select Tax returns.
4. Choose Change my return.
5. Select the tax year you want to correct.
6. Enter the revised information and complete the submission.
7. Save the confirmation number and summary of your changes.

In 2026, the CRA's current changing-a-return tool shows eligible years from 2016 to 2025. Returns for 2015 or earlier cannot be changed through Change my return.

Option 2: Use ReFILE through certified tax software

ReFILE lets eligible taxpayers amend an electronically filed T1 return using certified tax software. The original return must have been filed electronically through certified software.

You do not have to use exactly the same software that sent the original return, although the CRA notes that using the same software may be easier because your existing tax data may already be available.

For the 2026 NETFILE/ReFILE transmission period, the CRA states that ReFILE can transmit amended T1 returns for 2022, 2023, 2024 and 2025. The 2026 service is open from February 23, 2026 until January 29, 2027, subject to scheduled maintenance and other service interruptions.

When ReFILE is not available

The CRA identifies several ReFILE exclusions. You cannot generally use ReFILE for:

• a return outside the currently supported ReFILE years;
• a bankruptcy return or a year before the year of bankruptcy;
• an optional T1 return for a deceased taxpayer;
• a return filed using the incorrect province or territory of residence;
• most international or non-resident returns; or
• a return requiring Form T2203 because a business has a permanent establishment outside the taxpayer's province or territory of residence.

Professional EFILE preparers have some additional rules. For example, CRA guidance permits EFILE providers to use ReFILE for returning residents and immigrants starting with the 2023 tax year.

Option 3: Submit Form T1-ADJ by mail

If you cannot make the change online, or choose not to, use Form T1-ADJ, T1 Adjustment Request.

The form asks for information including your Social Insurance Number, the tax year being changed, your name and address, authorization information if applicable, the specific adjustment and revised amounts, and a daytime telephone number.

Mail the completed form and supporting documents to the CRA tax centre that handles your request. Keep a copy of the package for your records.

Supporting documents depend on how you submit the change

For an online request, the CRA's 2026 guidance says you generally should not try to attach supporting records when first submitting the change. If the CRA needs documents, it will contact you and give you a case number. You can then use that case number to submit documents electronically through your CRA account.

The CRA notes that more than half of online change requests are processed without needing supporting documents.

For a mailed T1-ADJ request, include the supporting documents with the form. The CRA requires documents supporting the entire amount involved, including evidence for amounts you originally claimed if those supporting records were not previously sent.

For example, if you originally claimed medical expenses and later discover additional eligible receipts, be prepared to support the full revised medical-expense amount, not just the new receipts.

How many years back can you change a tax return?

The normal online window is limited. In 2026, Change my return generally covers eligible returns from 2016 through 2025, while the active ReFILE service accepts amended returns for 2022 through 2025.

Older returns may sometimes be adjusted by mail, but the CRA states that a refund cannot be issued for an adjustment request made more than 10 calendar years after the end of the tax year. Requests outside normal reassessment periods can also take substantially longer to process.

Current CRA processing times for tax return changes

The CRA's current changing-a-return page lists the following processing times:

• Online request: within 2 weeks.
• Request by mail: within 16 weeks from receipt.

These are not guarantees for every case. The CRA says certain requests may take up to 33 weeks, including adjustments involving multiple returns, tax years beyond the normal three-year reassessment period, bankruptcy, a deceased taxpayer, loss carrybacks, elected pension splitting, or cases where additional information or documents are required.

International, non-resident and emigrant adjustments may also take longer.

What you receive after the CRA reviews the change

Once the CRA finishes reviewing your request, there are three possible results.

• All requested adjustments are accepted: you receive a notice of reassessment showing the changes.
• Only some adjustments are accepted: you receive a notice of reassessment showing the accepted changes and an explanation for the changes not made. A separate letter may also be issued.
• No adjustment is accepted: the CRA sends a letter explaining why it did not make the requested changes.

If the adjustment produces a refund, the CRA says the refund is issued once the change has been processed. If you want future CRA refunds deposited directly into your bank account, see the Helpydo guide to setting up or changing CRA direct deposit.

If you disagree with the reassessment

A tax return adjustment and a formal objection are different procedures. An adjustment is used to correct or add information to your own return. If the CRA issues an assessment or reassessment that you believe is wrong and you want to formally dispute it, you may need to file a notice of objection instead.

See the Helpydo procedure on filing an objection to a CRA income tax assessment or reassessment for the separate dispute process and its deadlines.

What if you forgot income or assets from an older year?

A normal adjustment can be used to report missing income on an assessed return. However, where an error or omission involves older unreported income or assets and may expose you to penalties, the CRA's Voluntary Disclosures Program may be relevant.

The CRA states that VDP relief is considered case by case and can apply where a taxpayer comes forward to correct errors or omissions that meet the program requirements. The mistake or omission must generally be at least one year or one reporting period past its filing due date. This is a separate program from an ordinary T1 adjustment.

Common mistakes to avoid

• Do not file a second complete return for a year that has already been filed.
• Do not submit an adjustment before receiving the notice of assessment.
• If one adjustment is already pending, wait for the CRA response before sending another change to that return.
• Use the correct tax year and tax-return line numbers.
• Include all known corrections in one request when possible.
• Do not attach documents to a new online adjustment unless the CRA requests them and gives you a case number.
• For a mailed T1-ADJ, include supporting documents for the full relevant amount where required, not only the incremental change.
• Do not assume ReFILE supports every prior tax year; the supported years change with each filing season.
• Do not use a tax-return adjustment to update information such as your address, direct deposit or marital status when the CRA provides a separate service for that change.
• Do not confuse an adjustment request with a formal objection to a CRA assessment.