- A T1 adjustment is a request asking the CRA to change specific figures on a personal tax return (T1) that has already been filed and assessed.
- - Use a T1 adjustment when you made the mistake and simply want the CRA to correct the numbers on your own return.
- You generally need your original assessment to reference before requesting a change to it.
Realizing you forgot a slip, misreported a deduction, or simply made a typo after you’ve already filed is more common than most people think — and it doesn’t require refiling your entire return from scratch. The T1 adjustment process exists precisely for this: a formal request to the CRA to fix a specific error on a return that’s already been assessed.
This article explains what a T1 adjustment is, how it differs from other CRA processes you may have heard of, and how to actually request one.
What Is a T1 Adjustment?
A T1 adjustment is a request asking the CRA to change specific figures on a personal tax return (T1) that has already been filed and assessed. It’s used for honest errors and omissions — a missed slip, an overlooked deduction, an amount entered incorrectly — not for disputing a CRA decision you disagree with.
T1 Adjustment vs. Notice of Objection: Don’t Confuse Them
These are two different tools for two different problems, and mixing them up wastes time.
- Use a T1 adjustment when you made the mistake and simply want the CRA to correct the numbers on your own return.
- Use a Notice of Objection when you disagree with a decision the CRA made — for example, a reassessment that denied a deduction you believe you were entitled to, or added an amount you dispute. A Notice of Objection is a formal, deadline-driven dispute process, not a simple correction request, and it must be filed within a specific window after the CRA’s assessment or reassessment.
If you’re not sure which situation you’re in, that uncertainty alone is a good reason to get advice before choosing a path — filing the wrong type of request can waste the time you have to act.
How to Request a T1 Adjustment
- Wait for your Notice of Assessment. You generally need your original assessment to reference before requesting a change to it.
- Identify exactly what needs to change. Pin down the specific line, slip, or amount, rather than requesting a vague "recalculation."
- Gather supporting documents. Any slip, receipt, or record backing up the correction should be ready to submit — the CRA can request it even if it isn’t required upfront.
- Submit the request. This can typically be done through the CRA’s online "change my return" service in your CRA account, or by mailing a completed adjustment request form along with your supporting documents to your tax centre.
- Wait for the reassessment. The CRA reviews the request and, if accepted, issues a Notice of Reassessment reflecting the correction. If the CRA disagrees with your requested change, you’ll be notified of that too.
What You’ll Need
- Your Notice of Assessment (or reassessment) for the year in question.
- The slip, receipt, or document supporting the correction.
- A clear explanation of what was wrong and what the corrected figure should be.
How Far Back You Can Go
The CRA can generally only reassess a return — including reassessing it because of your own adjustment request — within the normal reassessment period for that tax year. Outside that window, a reassessment (including one you’re asking for) is generally only possible if the CRA agrees misrepresentation or another exception applies. In practice, this means very old returns may be harder, or impossible, to adjust through this process — don’t assume you can go back indefinitely.
If the Correction Increases What You Owe
Not every T1 adjustment works in your favour. If you discover you under-reported income or over-claimed a deduction, submitting the correction yourself — rather than waiting for the CRA to find it — is generally viewed far more favourably and avoids the kind of penalty that applies to a deliberate omission. If the amount and circumstances are significant, this is also worth discussing against the Voluntary Disclosures Program, which exists specifically for taxpayers coming forward before the CRA catches an issue itself.
If the CRA Denies Your Adjustment Request
A denied adjustment request isn’t necessarily the end of the road. Depending on the circumstances, you may still be within the window to file a formal Notice of Objection if you believe the CRA’s decision was wrong — but that window is based on the original assessment or reassessment date, not on when your adjustment request was denied, so don’t let time slip by while waiting for an informal response.
Frequently asked questions
Can I make a T1 adjustment for more than one year at a time?
Yes, you can generally submit separate adjustment requests for multiple years, though each year is reviewed on its own and should reference its own Notice of Assessment.
How is a T1 adjustment different from just filing an amended return?
Canada’s system doesn’t use a separate "amended return" form the way some other countries do — a T1 adjustment request is the mechanism used to correct an already-filed and assessed T1 return.
What if my correction is just a simple math error the CRA should have caught?
Even simple errors generally need to go through the same adjustment request process; the CRA doesn’t automatically re-check assessed returns for arithmetic mistakes without a request.
Is there a fee to request a T1 adjustment?
Requesting a T1 adjustment through the CRA’s own process does not involve a government fee. If you engage a professional to help prepare or review the request, that’s a separate cost from the CRA process itself.
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