Common Tax Mistakes to Avoid in Canada 2025

Each year, tens of thousands of Canadians lose money or face CRA reassessments because of simple, avoidable tax mistakes. In 2025, the Canada Revenue Agency (CRA) and Revenu Québec are using advanced AI-powered systems to cross-check millions of tax returns with employer slips, bank data, and third-party financial records. Even one missing document, unreported income source, or incorrectly claimed deduction can trigger an audit or penalty that erases your refund—and your peace of mind.

Filing taxes in 2025 isn’t just about accuracy—it’s about strategy and compliance. Whether you’re an employee, self-employed, investor, or retiree, the smallest oversight can result in big financial consequences. At Mackisen CPA Auditors Montreal, we protect our clients by catching errors before the CRA does. Our professionals file every return with legal precision, ensuring your information is accurate, your credits are optimized, and your record is audit-proof.

Legal and Regulatory Framework

Income Tax Act (Canada)
Section 150(1): Mandates annual filing for all Canadian residents earning income.
Section 162(1): Imposes a 5% penalty plus 1% per month on late-filed taxes.
Section 163(2): Adds a 50% gross-negligence penalty on false or incomplete filings.
Section 230: Requires taxpayers to keep six years of supporting documentation.

Tax Administration Act (Quebec)
Requires provincial taxpayers to maintain parallel compliance with Revenu Québec and imposes penalties for inaccuracies or omitted information.

Mackisen ensures that every client’s federal and provincial filings are aligned perfectly, eliminating discrepancies that could trigger reassessment.

Key Court Decisions

Guindon v. Canada (2015): CRA penalties for false statements apply even if the mistake was unintentional.
Venne v. The Queen (1984): Filing errors, even made in good faith, do not excuse liability.
Jordan v. The Queen (2009): CRA interest continues to accrue automatically until full compliance is achieved.

These rulings confirm one truth: accuracy is not optional—it’s a legal obligation.

Top Tax Filing Mistakes to Avoid in 2025

1. Missing or Duplicate T4, T5, or RL Slips: CRA and Revenu Québec automatically match these slips—any discrepancy results in a reassessment.

2. Failing to Report Side Income or Freelance Earnings: The CRA now tracks online platform income (Uber, Airbnb, Etsy, etc.).

3. Overclaiming Home Office Deductions: Without receipts and workspace verification, claims are often denied during audit.

4. Incorrect RRSP and FHSA Reporting: Double-counting contributions or missing carryforwards can lead to lost deductions or overcontribution penalties.

5. Ignoring Foreign Income: All worldwide income must be declared, even if taxed abroad—CRA enforces this through global data-sharing (CRS/FATCA).

6. Inconsistent Federal and Provincial Filings: Quebec residents must ensure their Revenu Québec data mirrors CRA submissions.

7. Forgetting to Claim Carryforwards: Unused tuition, capital losses, and charitable donations can be carried forward for future savings.

8. Filing Late: Late returns lead to automatic interest and penalty accumulation.

Mackisen’s multi-stage review process ensures every form, slip, and credit is verified before submission, protecting you from audit exposure.

Mackisen’s Tax Protection and Accuracy Strategy

1. Comprehensive Document Check: We collect and reconcile every slip and statement from employers, banks, and CRA databases.

2. Error Detection Audit: Identify inconsistencies in deductions, income, and credits before filing.

3. Dual-Filing Verification: Align federal and Quebec data to prevent mismatched reporting.

4. Optimization Review: Maximize RRSP, TFSA, FHSA, tuition, and family credits while staying within compliance limits.

5. Audit-Ready Filing: Build a complete, defensible record with full documentation for CRA or ARQ verification.

Our proactive approach prevents penalties and ensures you receive every refund and credit you’re entitled to.

Real Client Experience

A Montreal consultant missed reporting $9,200 in side income and was reassessed $3,700 in taxes and interest. Mackisen reconstructed records, filed adjustments, and secured full penalty relief.
A family underclaimed tuition and childcare credits for two years. Mackisen recovered $6,300 in lost refunds through amended filings.

Common Questions

What happens if I file with missing slips? CRA will reassess your return once slips are matched to your SIN, often with penalties. Mackisen checks all CRA data before submission.
Can I fix a mistake after filing? Yes. We can file a T1 Adjustment (federal) or TP-1 Correction (Quebec) quickly before CRA issues a reassessment.
Do tax software programs catch all errors? No. CRA holds you—not your software—responsible for mistakes. Professional verification is essential.
How long should I keep tax records? Six years after the end of the tax year. Mackisen helps you store digital copies securely.

Why Mackisen

Accuracy is your best defense against CRA penalties. At Mackisen CPA Auditors Montreal, we don’t just file—we protect. Every return we prepare is reviewed by experienced CPA auditors and tax lawyers to ensure it meets every legal and financial standard.

We combine technical precision with human care. Our mission is to keep you compliant, confident, and stress-free—no matter how complex your tax situation.

Call Mackisen CPA Auditors Montreal today for your 2025 Tax Filing Review. The first consultation is free, and your protection starts immediately.