If you’ve already filed and spot a mistake, wait for your notice of assessment, then use Change My Return in CRA My Account. Most online requests are processed within two weeks, while a mailed Form T1-ADJ has a longer service standard. Paper filing of a first return is still allowed if you can’t use NETFILE, but it takes roughly 12 weeks.
Wait for the assessment first
The CRA says you need your notice of assessment (NOA) before you ask for a change. Until then, the return is still being processed, and a change request has nothing to attach itself to. If you filed last week and found a missing slip, sit tight.
The NOA is the letter or online notice that shows how the CRA read your return: income, deductions, refund or balance owing. Read it against what you filed. Small differences often explain themselves, and some are the CRA’s own adjustments, which you’d handle through a notice of objection instead (usually within 90 days). For notices and unfiled returns generally, see our guide to CRA notices and unfiled returns.
What you can change
A change request covers things you reported or left out. Typical examples are a missing T4 or other slip, an RRSP contribution receipt you forgot, child care costs, or medical expenses. You can also correct an amount you got wrong.
Some things can’t be handled this way at all. The CRA lists applying for benefits or credits, making or revising an election, and updating personal details such as your address or marital status. Those go through other channels.
Change My Return in My Account
This is the fast route. Sign in to your CRA account, choose the tax year, and follow the Change My Return prompts. If you use certified tax software, its ReFILE service does the same job online.
The CRA reports that most online requests are processed within two weeks, and it says more than half are handled without any supporting documents. Two tools help you track the request: the check processing times tool and the progress tracker inside your account. If you’re locked out or haven’t registered, our CRA My Account sign-in guide covers it.
The online option has limits. The CRA says you can’t use it for some situations, including returns for a bankrupt or deceased taxpayer, a wrong province of residence, and certain non-resident returns. Older years are limited too: My Account works back to 2015 and ReFILE only back to 2021. For those cases you’ll use paper.
Form T1-ADJ by mail
Form T1-ADJ, the T1 Adjustment Request, is the paper version. You can also send a signed letter with the same details. Mail it to your tax centre, and send it separately from any return for the current year. For Toronto residents that’s the Sudbury Tax Centre, 1050 Notre Dame Avenue, Sudbury ON P3A 5C2.
The form asks for your Social Insurance Number, the tax year, your name and address, your daytime phone number and a description of each change. You need supporting documents for the whole amount you’re claiming.
Documents to attach
Online, you only send documents if the CRA asks. Once you have a case number, you can upload them through your account. By mail, attach everything up front. Send copies, not originals.
- A copy of the missing or corrected slip (T4, T5, T3, T4A and so on)
- Receipts for RRSP or FHSA contributions, donations, child care or medical costs
- A short note that says what changed and by how much
Worked example: your NOA shows a $3,200 refund, and you then find a $2,000 RRSP receipt. Add it through Change My Return and keep the receipt ready. If your combined federal and Ontario marginal rate is around 30%, the deduction could be worth roughly $600 more. Test your own numbers with the income tax calculator before you ask.
How long adjustments take and the time limit
Online, plan on about two weeks. By mail, the CRA’s 2026 tax tip cites an eight-week service standard, down from about 30 weeks at the 2025 peak. An older CRA page still says 16 weeks, and complex cases can take up to 33 weeks. The numbers differ between pages, so check the CRA processing times tool before you count on a date.
There’s a limit on age. Refunds generally can’t be issued for adjustments requested more than 10 calendar years after the tax year ends. And if the change means you owe more, don’t wait. Interest runs on what you owe, so fix it early.
When paper filing is allowed
Most people file with certified software and NETFILE. The CRA’s position is that if you can’t use NETFILE, you can print and mail your completed return. Paper is also how some older years and special cases are filed.
Since 2025 the CRA no longer mails tax packages automatically. You have to request one. The deadline is the same as online: April 30 for most people, June 15 for the self-employed, with any balance still due April 30. Late filing costs 5% of the balance plus 1% per full month, up to 12 months. See the late-filing penalty and relief guide for how to ask for relief.
Where to mail it and why it’s slower
Paper is the only way to send a paper return, and it goes by mail to your tax centre. Toronto residents use the Sudbury Tax Centre address above (the CRA lists Barrie, Belleville, Kingston, Ottawa, Peterborough, St. Catharines, Sudbury and Toronto under it). Check the CRA page for your own situation, because self-employed filers and non-residents may have different rules.
The CRA says paper returns are usually processed within 12 weeks. That’s because someone has to open, sort and enter the return by hand, while a NETFILE return arrives already in digital form. Refunds follow the same wait. Direct deposit helps, but it can’t fix the processing time.
Getting proof of filing
The CRA’s own proof is the notice of assessment. It confirms the return was received and tells you the result. You can also see your assessment in My Account.
The CRA pages reviewed for this article do not describe a mailing receipt or postmark rule for T1 returns. If proof of the mailing date matters to you, ask Canada Post for a tracked service and keep a full copy of what you sent. That’s a practical step, not a CRA requirement.
Sources
- Changing a tax return
- Making changes to your tax return, CRA tax tip 2026
- Form T1-ADJ, T1 Adjustment Request
- Filing a paper tax return
- Where to mail your paper T1 return
Common questions
Can I change My Return before I get the notice of assessment?
How long does a change to a return take?
Do I need to send documents when I change My Return online?
Where do Toronto residents mail a paper return?
How far back can a change be requested?
Last reviewed: . Figures come from the official sources listed above. How we check the numbers and our editorial policy.