A Notice of Reassessment means the CRA has changed a return it had already assessed. Most are resolved quickly once you understand what the CRA changed and why, and the reason is usually one of a short list: a slip that doesn’t match the return, an unusually large claim, or an adjustment you asked for yourself. This page covers those reasons and what the CRA can reassess; it is part of the Dealing with the CRA directory.
Types of CRA adjustments
| Type | What It Means |
|---|---|
| Reassessment | CRA changed your return |
| Adjustment | You requested a change |
| Audit assessment | Result of review/audit |
| Arbitrary assessment | CRA filed for you |
An arbitrary assessment follows a return that was never filed; what leads to one is covered in what happens if you don’t file your taxes. An audit assessment follows a review or audit letter, covered in what to do when you get a CRA audit letter.
How a reassessment is different from an audit
| Notice of Reassessment | Full Audit | |
|---|---|---|
| Trigger | Specific slip mismatch or data discrepancy | Broader review of your return |
| Scope | Usually one or two line items | All items or specific topic (e.g., all business expenses) |
| Process | CRA makes change; you can object | CRA requests documents; you respond |
| Common outcome | Balance owing or refund adjustment | Similar outcome, but via different process |
| Time to resolve | Weeks to months | Months to over a year |
Top triggers: the most common reassessment causes
1. T-slip mismatches (most common)
CRA receives your T4, T5, T3, and T5008 slips directly from your employer, bank, and investment firm. These are cross-matched to your return. Common mismatches:
| Slip | What CRA checks |
|---|---|
| T4 | Employment income matches Box 14 on your return |
| T5 | Dividend and interest income matches investment income |
| T3 | Trust income (mutual funds, ETFs) reported correctly |
| T5008 | Proceeds of disposition match capital gains reported |
| T4A | Contract payments, pension income, CERB/CRB reported |
2. One-time large claims
Unusually large claims relative to your income level can trigger review:
- Charitable donations above 75% of net income
- Home office expenses disproportionately large versus employment income
- Business losses claimed for multiple consecutive years
- Large medical expense claims without supporting receipts
3. T1-ADJ you filed yourself
If you submitted a T1 amendment to add a missed RRSP deduction, child care expense, or other credit, CRA processes this as a reassessment. It typically takes 8–12 weeks and may generate an additional refund if approved; how to file one is covered in changing a filed return with the T1-ADJ.
Common reassessment reasons at a glance
| Reason | Example |
|---|---|
| Disallowed deduction | RRSP over-contribution |
| Income addition | Unreported T4/T5 |
| Credits denied | DTC not approved |
| Audit adjustment | Business expenses disallowed |
| Error correction | Math mistakes |
What makes a return more likely to be picked for a broader review is covered in CRA audit triggers.
What the CRA can and cannot reassess
| CRA can reassess | CRA cannot reassess |
|---|---|
| Any return within the 3-year normal reassessment period | Returns older than 3 years (absent fraud) |
| Returns where fraud or misrepresentation is alleged (any year) | Returns already upheld by Tax Court |
| Returns with unreported foreign income (extended periods) | Matters already resolved by formal agreement |
| Returns flagged by third-party slip mismatches | n/a |
Foreign property reporting on Form T1135 is one source of extended periods; who must file it is covered in the T1135 guide.
Interest on a reassessed balance
The CRA charges interest on reassessment balances from the original April 30 filing deadline of the tax year in question, not from the date of the reassessment notice. The rate is the prescribed rate in effect for each quarter (7% as of Q4 2026; the history is on the CRA prescribed interest rate page).
This means interest can already be substantial when the notice arrives. For example, if a reassessment adds $4,000 of tax to a return filed three years earlier , interest has been accumulating on that $4,000 since the day after that year’s April 30 balance-due date, which adds to the amount owing before you open the letter. Paying the balance on receipt, even with an objection planned, stops further interest, and if the objection succeeds the CRA refunds the payment with interest. How an unpaid reassessment moves to collections is covered in what happens if you don’t pay the CRA.
If you disagree
A Notice of Objection filed within 90 days of the reassessment date is the formal route, with an extension possible under Income Tax Act subsection 166.1 and the Tax Court of Canada after that. The deadlines, the extension conditions and the Tax Court procedures are on the guide to disputing a CRA assessment.
Records that support a return
Documentation is what settles most reassessments:
- T-slips (T4, T5, T3, T5008), kept for 7 years
- Receipts for all deductions claimed (medical, donations, childcare, moving, employment expenses)
- For capital gains: a running adjusted cost base (ACB) record for all investments
- For self-employment: invoices, receipts, and mileage logs for the full 3-year reassessment window plus a margin
- For foreign property: the annual T1135 if total cost exceeds $100,000, since a missed form extends the reassessment period
Related CRA guides
- Reading your Notice of Assessment: the sections a reassessment changes
- Checking whether you owe the CRA: where a reassessed balance shows up
Sources
The figures and rules on this page come from these sources, last checked against them on September 29, 2026. How we check facts.
- Canada Revenue Agency: Prescribed interest rates