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If you spot an error after you file, ask the CRA to change the return you already sent. Wait until you get your notice of assessment, then use the change my return option in your CRA account or mail Form T1-ADJ. The CRA says online requests are usually processed within about 2 weeks, and mailed ones within about 20 weeks.
How do you change a return?
- Wait until you get your notice of assessment, so the CRA has finished the first one.
- Sign in to your CRA account and use the change my return option, or send the T1 adjustment request by mail.
- Say what changed, and attach any slips or receipts for the new amounts.
If you already asked for a change, wait for the CRA’s answer before you ask for another. If you used certified tax software, the CRA also offers an online service called ReFILE. By mail, send Form T1-ADJ to your tax centre separately from your current-year return, with documents that back up the full amount you are claiming.
What can you change with a change request?
You can report income you missed, such as a T4 or tips, claim deductions, credits or expenses, or add a slip, such as an RRSP receipt. You cannot use a change request to apply for benefits or credits, to make or revise an election, or to update your address, direct deposit or marital status. Those go through other CRA channels.
What if the mistake means you owe more?
Fix it as soon as you can. The CRA may charge interest on the extra tax. For a bigger omission, ask about the CRA’s Voluntary Disclosures Program, which offers relief case by case to people who come forward to correct errors or omissions.
What if the mistake means you are owed money?
You can generally ask for a change for up to 10 calendar years back, so a missed credit or slip can still be claimed. The CRA says no refund is issued for an adjustment requested more than 10 calendar years after the end of the tax year. Keep receipts for the years you ask about.
What will the CRA send back?
If the CRA agrees, you get a notice of reassessment showing the changes. If it agrees to part, the notice shows what changed and why the rest did not. If it makes no change, you get a letter explaining why. Some requests take longer, up to 36 weeks, for example when they cover several years or years beyond the normal reassessment period. If you disagree with the answer, the objection route is in the page on CRA letters.
What should you watch out for?
A mismatch with a slip can trigger a letter. See our CRA letters decoder and dealing with the CRA. If the mistake is a missing slip, what to do about a lost slip covers it. A tax preparer can help with bigger corrections.
Where does this information come from?
The steps follow the Canada Revenue Agency guidance on changing a tax return. Checked in October 2026. This is an independent information site: we provide no services, we do not represent the CRA or any organization, and we do not guarantee that anything here is accurate or current. We accept no liability for decisions based on it. Check the official source before you rely on it. See the full disclaimer.
Frequently asked questions
How do I fix a mistake on a tax return I already filed?
Wait for your notice of assessment, then sign in to your CRA account and use the change my return option, or mail Form T1-ADJ. Say what changed and attach slips or receipts for the new amounts. Do not ask for another change until the CRA answers the first.
How long does it take the CRA to process a change to my return?
The CRA says online requests are usually processed within about 2 weeks and mailed requests within about 20 weeks. Complex requests, such as several years at once, can take up to 36 weeks.
How far back can I change my tax return?
You can generally ask for a change for up to 10 calendar years back. The CRA says it will not issue a refund for an adjustment requested more than 10 calendar years after the end of the tax year, even if the request itself is accepted.
Can I change my address or marital status with a return change request?
No. The CRA says a change request cannot be used to update your address, direct deposit or marital status, or to apply for benefits and credits. Those updates are made separately in your CRA account.
What if I forgot to report income and now owe more tax?
Fix it as soon as you can, because interest can build on the extra tax. The CRA's Voluntary Disclosures Program offers relief case by case to people who come forward to correct errors or omissions, so ask about it for a larger omission.