You disagree with your CRA Notice of Assessment (or Reassessment). You have two formal paths to fix it: a T1 Adjustment Request (informal, fast, free) or a Notice of Objection (formal, slow, preserves appeal rights). This guide walks you through both, in the order you should try them.

Step 1 — be sure CRA is actually wrong

Before you file anything, do this: open the NOA's Explanation of changes section, identify the exact line CRA changed, and pull your supporting documents. About 60% of "CRA is wrong" disputes are actually missing T-slips or misread receipts on the taxpayer's side. We cover how to read the explanation in the NOA line-by-line guide.

If after that you're still convinced CRA made an error, decide which form to file based on the dollar amount and complexity:

• Under $5,000 and clearly a T-slip, deduction, or credit issue: file a T1 adjustment
• Over $5,000, or interpretive (CRA disallowed a claim on principle): file a Notice of Objection
• CRA denied your T1 adjustment: file a Notice of Objection within 90 days of the denial letter

Step 2A — file a T1 adjustment (the easy path)

T1 adjustments are CRA's pressure-relief valve for "small fix" disputes. Three ways to file:

1. CRA My Account → Tax returns → Change my return. Pick the year, find the line, type the new number, attach a PDF of your supporting document. Median processing: 2 weeks online, 8 weeks with attachments.
2. ReFILE through your tax software (Wealthsimple Tax, TurboTax, UFile all support it). Best when the change rolls into multiple lines automatically.
3. Form T1-ADJ on paper. Slowest path. Don't bother unless you have no CRA My Account.

T1 adjustments don't have a strict deadline, but CRA's discretion ends at 10 years from the original NOA date. Inside that window CRA generally accepts well-documented requests.

Step 2B — file a Notice of Objection (T400A)

The formal dispute. This is what you file when CRA disallows a major claim, applies the General Anti-Avoidance Rule, or interprets a section of the Income Tax Act differently than you do.

Three ways to file:

1. CRA My Account → Submit documents → Register a formal dispute (online objection). Easiest, dated automatically.
2. Form T400A mailed or faxed to your local CRA Appeals Intake Centre. Use this if you need to attach a long submission.
3. A letter stating "Notice of Objection" with the relevant tax year, the assessment date, the issue in dispute, and the relief sought. Less common, accepted by CRA.

Whichever form you use, include: the tax year, the date of the assessment/reassessment, your SIN, the specific line items you're disputing, the dollar amounts, the legal or factual basis for your position, and PDFs of supporting documents.

Step 3 — what happens next

1. CRA Appeals acknowledges the objection within 30 days (a one-page confirmation letter).
2. An Appeals Officer is assigned. They are independent from the auditor or assessor who made the original decision.
3. The officer contacts you by phone or letter — typically 4–8 months after filing for low-complexity files, 12+ months for complex files.
4. You exchange documents until the officer reaches a decision: confirmed (CRA wins), varied (partial), or vacated (you win).
5. You receive a Notice of Confirmation, Variation, or Vacation — the final administrative decision.

Median timelines from CRA's 2024 service standards: 12 months for low-complexity files, 24+ months for complex files. Set expectations accordingly.

Step 4 — escalating to Tax Court

If you lose the objection (or 90 days pass with no response), you can appeal to the Tax Court of Canada. Two procedures:

• Informal Procedure — disputed federal tax + penalty under $25,000 per year, or under $50,000 in disputed losses. Self-representation allowed, no formal rules of evidence, hearings often within 6 months.
• General Procedure — anything larger, or any GST/HST appeal. Lawyer effectively required, formal pleadings, longer timeline.

Tax Court hearings happen in major cities across Canada. You don't have to travel to Ottawa.

Step 5 — taxpayer relief (the parallel track)

Notice of Objection is for disputing the underlying tax. Taxpayer Relief (form RC4288) is for waiving interest and penalties when the tax itself is correct but you have a hardship case: serious illness, financial hardship, CRA error or delay, or natural disaster.

Taxpayer Relief is granted at CRA's discretion — there's no appeal beyond a second-level review and then the Federal Court. Use the late filing penalty calculator to estimate what's at stake before filing.

Bottom line

Try a T1 adjustment first — it's faster, free, and resolves most disputes. File a Notice of Objection if CRA denies the adjustment, the dollar amount is large, or the issue is interpretive. The 90-day clock on objections is strict, so don't wait. And whatever you do, don't let an unpaid disputed balance sit accumulating 8% interest if you can pay first and get refunded later — sometimes the cheapest path is to disagree on paper and comply on the cheque.

Related reading: reassessment vs assessment, review letter vs audit vs reassessment.

Sources: CRA — File a Notice of Objection, CRA — Form T400A, Tax Court of Canada.