Introduction

Every year, millions of Canadians file their taxes on their own using DIY software or free online tools. While this may seem cost-effective, many taxpayers unknowingly leave money on the table or worse, expose themselves to CRA reassessments, penalties, and missed credits. DIY tax filing often overlooks complex deductions, changing rules, and industry-specific nuances. This guide explains the hidden costs of filing your taxes alone and why working with a CPA near you in Montreal can actually save you money.

Legal and Regulatory Framework

Under the Income Tax Act and the Taxation Act of Quebec, taxpayers are required to:
• Report all sources of income
• Claim only eligible deductions
• Comply with GST/QST when self-employed
• Maintain documentation for at least six years
• Apply the correct rules for tuition, medical expenses, moving expenses, rental income, investments, and business expenses

DIY software does not take responsibility for errors. CRA and Revenu Québec hold you, the taxpayer, fully accountable.

Mistakes in compliance can lead to:
• Denied deductions
• Lost credits
• Reassessments
• Interest and penalties

Key Court Decisions

Courts have repeatedly ruled that:
• Taxpayers cannot blame software for filing mistakes
• Misinterpretation of the law is not a valid defense
• Missing documentation means deductions will be denied
• CRA can reassess based on bank deposits and third-party data if your return appears incorrect

Judges consistently confirm that professional responsibility lies with the taxpayer — unless a CPA is retained to ensure compliance and accuracy.

Why CRA Targets DIY Filers

DIY tax returns often contain errors that trigger audits, including:
• Unreported self-employment or gig income
• Incorrect home office claims
• Misclassified employment expenses
• Missed tuition or moving credits
• Incorrect rental or investment reporting
• Inconsistent numbers vs. third-party slips
• GST/QST errors for freelancers or small businesses

CRA electronically matches tax returns with employer slips, school statements, banks, financial institutions, and payment platforms.

The Hidden Costs of DIY Taxes

1. Missed Credits and Deductions

DIY software cannot ask smart follow-up questions or interpret your situation like a CPA. Many taxpayers miss:
• Medical expense credits
• Tuition and education transfers
• Disability credits
• Childcare deductions
• Moving expenses
• Home office calculations
• Business-use-of-home deductions
• Investment and rental property write-offs

These missed opportunities often exceed the cost of hiring a CPA.

2. Overpaying Taxes Due to Incorrect Inputs

Tax software only calculates what you enter. If you misunderstand a category, mislabel income, or forget a slip, the return becomes inaccurate — and CRA won’t correct it for you.

3. Higher Audit Risk

DIY returns often include red flags because:
• Numbers don’t match third-party data
• Cash income is missing
• Deductions are inconsistent
• GST/QST is misapplied
• Expenses lack documentation

Audits can cost thousands in time, stress, and penalties.

4. Penalties for Simple Mistakes

Even honest mistakes — wrong RRSP limit, misreported tuition, misclassified income — can lead to reassessments with interest. DIY users frequently discover errors months or years later.

5. No Strategy for Future Years

DIY returns focus on the current year only. A CPA:
• Optimizes for next year
• Advises on RRSP contributions
• Plans for business, rental, or investment growth
• Manages carry-forward credits
• Helps avoid tax bracket spikes
• Advises on incorporation when relevant

DIY software cannot do long-term planning.

Mackisen Strategy

At Mackisen CPA Montreal, we help taxpayers eliminate the risks of DIY filing by:
• Preparing accurate, optimized tax returns
• Identifying missed deductions and credits
• Correcting past mistakes and filing adjustments
• Reducing audit risk through compliant filings
• Advising on personal and business tax strategies
• Providing support in case of CRA or Revenu Québec reviews

We ensure your taxes are not only filed — but filed correctly.

Real Client Experience

A Montreal professional filed her own taxes for three years and missed over $2,500 in tuition credits. We corrected the returns, reclaimed the refunds, and optimized her future filings.
Another client incorrectly reported rental income and deducted personal expenses; CRA reassessed him for over $3,000. We rebuilt the returns, negotiated penalties, and established a proper bookkeeping method.

Common Questions

Isn’t tax software accurate?

Software is accurate only if your inputs are accurate. Most mistakes come from misunderstandings, not the software.

Can a CPA find deductions I missed?

Yes. CPAs apply tax law not just software rules — and routinely uncover missed credits.

What if I already filed incorrectly?

We can adjust returns for up to 10 years in many cases.

Isn’t hiring a CPA expensive?

Not compared to the cost of missed deductions, penalties, or reassessments.

Why Mackisen

With more than 35 years of combined CPA experience, Mackisen CPA Montreal helps individuals save money, avoid penalties, and gain peace of mind through accurate, compliant tax filing. Our expertise ensures your return is optimized, complete, and audit-ready.