How do I dispute a CRA tax assessment?

File a formal Notice of Objection within 90 days of your Notice of Assessment date. Do this through My Account online, by filling out Form T400A, or by writing a letter. Include the tax year, issues disputed, facts, and reasons for your objection.

What is the deadline to dispute a CRA assessment?

You have 90 days from the date on your Notice of Assessment or Reassessment to file a Notice of Objection. If you miss this deadline, you can apply for an extension within one year, but must show valid reasons.

Can I dispute a CRA assessment without a tax professional?

Yes, you can represent yourself. For simple disputes (clear errors, forgotten deductions), self-representation often works. For complex issues involving interpretation of tax law or large amounts, consider hiring an accountant or tax lawyer.

How to Dispute a CRA Assessment or Reassessment in Canada (2026)

When to Dispute CRA

Situation	Should You Dispute?
CRA disallowed a legitimate deduction	Yes
Math error on your return	Start with amendment, then dispute if rejected
CRA reassessed previous years	Yes, if you disagree
Penalty you believe is unfair	Can request relief under Taxpayer Relief Provisions
Disagree with CRA’s interpretation	Yes
Made a mistake on your return	File an adjustment request (T1-ADJ), not objection

Dispute Timeline Overview

Step	Timeline
1. Receive Notice of Assessment	Day 0
2. Review and gather documents	Days 1-30
3. Consider calling CRA first	Before 90 days
4. File Notice of Objection	Within 90 days
5. CRA reviews objection	3-12+ months
6. Receive decision	After review
7. Appeal to Tax Court (if needed)	Within 90 days of decision

Step 1: Review the Notice of Assessment

What to Check	Details
Assessment date	Your 90-day deadline starts here
Amounts changed	Compare to what you filed
Explanation	Read CRA’s reasoning
Line-by-line comparison	Check against your return

Step 2: Gather Supporting Documents

Document Type	Examples
Receipts	Medical, charitable, childcare
T-slips	T4, T5, T4A you included
Correspondence	Letters from CRA
Calculations	Worksheets showing your math
Third-party proof	Bank statements, employer letters

Step 3: Try Informal Resolution First

Before filing a formal objection, consider calling CRA:

Method	Phone
Individual inquiries	1-800-959-8281
Business inquiries	1-800-959-5525

What to ask	Details
Explanation	Why was my assessment changed?
Error correction	Can this be fixed without formal objection?
Additional info	What would you need to reconsider?

Step 4: File a Notice of Objection

Three Ways to File

Method	How
My Account	Register a formal dispute online (fastest)
Form T400A	Mail or fax completed form
Letter	Write your own letter with required information

Required Information

Include	Details
Your name and address	As it appears on assessment
Social Insurance Number	Required identifier
Tax year(s)	Which years you’re disputing
Relevant facts	What happened, what you claimed
Reasons for objection	Why you believe you’re correct
Supporting documents	Copies of evidence

Sample Objection Letter

[Your Name]
[Your Address]
[City, Province, Postal Code]

Date: [Today's Date]

Canada Revenue Agency
[Address from your Notice of Assessment]

Re: Notice of Objection
    Tax Year: 2024
    SIN: XXX-XXX-XXX

I hereby file a Notice of Objection to my Notice of Assessment 
dated [date] for the 2024 tax year.

Issue: [e.g., Disallowed medical expense deduction of $5,000]

Facts:
[Describe the situation clearly]

Reasons:
[Explain why you believe your position is correct,
referencing tax law if applicable]

Enclosed: [List supporting documents]

I request that you vacate/vary the assessment as follows:
[What you want CRA to do]

Sincerely,
[Your signature]
[Your printed name]

Where to Send

If you live in…	Send to…
Atlantic Canada	Summerside PE
Quebec	Shawinigan QC or Jonquière QC
Ontario/Nunavut	Sudbury ON
Prairie provinces	Winnipeg MB
BC/Yukon/NWT	Surrey BC

Check CRA website for current mailing addresses.

What Happens After Filing

Stage	What Happens
Acknowledgment	CRA confirms receipt (usually)
Review	Appeals officer examines your case
Contact	May ask for more information
Decision	CRA will allow, partially allow, or deny
Timeline	3-12+ months (often longer for complex cases)

If CRA Denies Your Objection

Option	Timeline
Accept the decision	No further action
Appeal to Tax Court	Within 90 days of decision
Informal procedure	For amounts under $25,000 federal tax
General procedure	For larger amounts (lawyer recommended)

Taxpayer Relief Provisions

For penalties and interest (not the underlying tax), you can request relief:

Form	Purpose
RC4288	Request taxpayer relief
Grounds	Extraordinary circumstances, CRA delays, financial hardship
Timeline	Can request for past 10 years

When to Get Professional Help

Situation	Professional
Simple factual dispute	Self-represent or accountant
CRA error	Self-represent
Interpretation of tax law	Tax accountant or lawyer
Large amounts (>$10,000)	Definitely get help
Going to Tax Court	Tax lawyer
Potential criminal issues	Tax lawyer immediately