Notice of Reassessment
The CRA changed a return you already filed — usually a slip mismatch (a T4/T5 they received that you didn't report) — and it typically comes with a balance owing plus back-dated interest.
⏰ The deadlines
| Formal objection | 90 days from the reassessment date — individuals get until 1 year after the return's filing due date if later |
| Late objection | Extension possible up to 1 year after the 90-day deadline, but it's discretionary — don't rely on it |
| Interest | Compounds daily, back-dated to the original due date |
✅ How to defuse it: Filing a formal objection on time ("Register my formal dispute" in My Account, or form T400A). Collection of the disputed income-tax amount is generally paused while the objection is under review.
🛡️ Defenses & defects to check
- If the reassessment is simply missing information (a receipt they didn't have), a T1 adjustment or a reply to the letter often fixes it faster than a formal objection.
- Check the CRA's math against your slips — matching-program reassessments are automated and do contain errors.
- An appeals officer independent of the original team reviews objections and can confirm, vary, or vacate the assessment.
💡 What the pros know
- The 90-day window is the single most important deadline in Canadian tax life. Calendar it minus a week the day the notice arrives.
- Paying the disputed amount while objecting stops interest from growing if you lose — you get it back with interest if you win.
Related forms: Notice of Assessment (NOA) · Collections Letters (Reminder → Legal Warning) · Taxpayer Relief (Your Request — Form RC4288)
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Decode it freeGeneral tax information, not tax or legal advice — verified against official guidance but programs and deadlines change. Confirm on canada.ca or with a licensed tax professional; free help exists at community tax clinics (CVITP).