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An income tax assessment is the CRA’s answer to your return. It’s called a notice of assessment, and it tells you what tax you owe or what refund you get, line by line. If you filed electronically, it’s usually available in your CRA account as soon as the return is processed. Read it, and keep it. It’s the paper you’ll want if anything about your tax gets questioned later.
Most notices are dull. That’s the good outcome. The trouble starts when the numbers on it don’t match what you filed.
What does the notice of assessment show?
The notice includes your name and address, the last four digits of your SIN, the assessment date and an account summary that says refund or balance owing. Below that comes the calculation, line by line. It also carries an eight-character NETFILE access code.
| Part of the notice | What to check |
|---|---|
| Account summary | Refund or balance owing matches what you expected |
| Line-by-line amounts | Each line equals what you reported |
| Explanation of changes | Any line the CRA adjusted, and why |
| NETFILE access code | Present on the notice, so note where it is |
Compare the notice with your copy of the return. Agree? Then you’re done. If a line differs, the explanation section says what the CRA changed. To sanity-check your expected result before you file, try the tax refund calculator.
How do you get your assessment?
The CRA says to sign in to your CRA account, and that is the quick route. You can also see notices from earlier years there. If you can’t get online, you can ask for a paper copy by calling 1-800-959-8281. Paper returns take longer to process, and so does a return that was filed late or is under review.
The CRA has also said that from 9 February 2026 notices of assessment and reassessment are viewed in its portals right after processing. We couldn’t confirm from the pages we read whether a paper copy is still mailed automatically, so don’t wait for the mail.
What if the assessment is wrong?
There are two paths, and they aren’t the same. If you left something out, such as an RRSP receipt or a slip, you ask the CRA to change your return. If the CRA changed something and you disagree even with complete information, you file a formal dispute, and the deadline is 90 days from the date on the notice.
To change a return you need your notice of assessment first. Use “Change my return” in your CRA account, or the ReFILE feature in certified tax software, and the CRA lists about two weeks for online requests. By mail you send form T1-ADJ, and it lists about 19 weeks, with some complex requests taking up to 35. The CRA won’t refund an adjustment for a year older than 10 calendar years.
Here’s what a missed slip is worth. Say you earn $70,000 in Ontario and forget a $2,000 RRSP receipt. Your taxable income should have been $68,000 (before other deductions). Our engine puts the tax difference on $2,000 at about $593, which is 29.65% at that income. It’s a rough figure without other credits. The RRSP calculator and the marginal tax rate calculator show how the number moves at other incomes.
What is a notice of reassessment?
It looks like the first notice and it means the CRA or you changed the return after it was assessed. The CRA only sends one when something changed. For individuals, the normal reassessment period is three years from the mailing date of the original notice, though the CRA can go back further where there’s neglect, carelessness or fraud.
So keep your receipts at least until those three years have passed, and check the CRA’s record-keeping page for the exact rule. A reassessment isn’t automatically an audit. A late slip or your own correction can trigger one.
Mistakes that cost people money
Ignoring the notice is the first. Balances owing don’t disappear because you didn’t open it. The second is assuming a low refund means you did something wrong. The refund depends on how much tax was taken off during the year and on credits, and the income tax calculator shows the tax on your income so you can compare it with what came off your pay.
The third is filing a fix through the wrong channel. A dispute and a change request are different things, and only one of them has a 90 day clock.
Where the numbers come from
The contents of the notice, the 90 day dispute period, the processing times and the 10 year limit come from Canada.ca pages published by the CRA. The three year reassessment period comes from CRA guidance for individuals. The tax example uses our 2026 federal and Ontario rates. This site isn’t linked to the CRA.
Frequently asked questions
What is an income tax assessment?
It's the CRA's processed result of your return, shown on a notice of assessment with your refund or balance owing and the line-by-line calculation.
How long do I have to dispute an assessment?
The CRA says 90 days from the date of the notice to register a formal dispute.
How do I change a return after I get my assessment?
Wait for the notice, then use Change my return in your CRA account, ReFILE in certified software, or mail form T1-ADJ.
What is a notice of reassessment?
It's an updated notice the CRA sends when it or you changed the return after the first assessment. It explains what changed.
How far back can the CRA reassess an individual?
The normal period is three years from the mailing date of the original notice. It can go further back if there is neglect, carelessness, wilful default or fraud.
- How to file your tax return in Canada: steps and dates
What to gather, when your return is due and how to file in Canada, from the first slip to the notice of assessment that closes the year
Information only. This page is general information, not tax, legal or accounting advice. Tax-Services.ca is an independent publisher: we don't prepare or file tax returns or offer tax services, and we have no connection with the CRA, Revenu Québec, any government or any company named on this page. Check the figures that matter with an official source or a qualified professional.