Fixing a mistake on a medical claim

Mistakes happen. Whether it’s an overlooked receipt, an ineligible expense, or a miscalculation on your return, medical expense errors are among the most common tax filing issues—and fortunately, they’re also among the easiest to fix.

This matters when you’ve claimed too much, too little, or included an expense in the wrong year. Correcting the error not only helps you stay compliant with CRA rules, it ensures you receive every dollar you’re entitled to without delay or future reassessment.

Here’s how to identify and fix a medical expense mistake on your return, and what to expect from the correction process.

Common Medical Claim Errors

Errors can take several forms, including:

• Claiming ineligible expenses
  These may include cosmetic procedures, over-the-counter drugs without a prescription, or travel costs that don’t meet CRA distance rules.

• Claiming the same expense twice
  Some taxpayers accidentally include a cost in two different years or under both spouses’ names.

• Missing expenses you forgot to claim
  A misplaced receipt or delay in receiving an invoice can lead to under-claiming.

• Using the wrong 12-month period
  Choosing overlapping or inconsistent claim windows can result in expenses being rejected.

• Incorrect threshold calculation
  Failing to apply the 3% of net income (or the fixed CRA threshold) can affect the claimable amount.

How to Make a Correction: Step-by-Step

If you filed your return and later realize your medical claim was incorrect, you can fix it using one of the CRA’s adjustment methods.

Ways to Correct a Medical Claim Error

What Happens After You File a Correction

Once the CRA receives your adjustment, they will:

• Review your updated information and compare it with your original claim

• Request supporting documents if needed (such as receipts or proof of medical necessity)

• Issue a Notice of Reassessment showing the corrected calculation, and any refund or balance owing

This process can take anywhere from two to eight weeks, depending on complexity and whether documents are requested.

Documentation to Include With Your Correction

The CRA may request, or you may proactively include:

• Original receipts showing the amount paid, service provided, and patient’s name

• Letter or prescription from a medical professional (for travel, devices, or attendant care)

• Explanation of the change, especially if the error was due to a calculation or period selection

Keep all supporting materials on hand for six years even after the correction is made.

When Not to Submit a Correction

There are a few situations where a correction is unnecessary:

• Your return hasn’t been assessed yet
  You can wait for your Notice of Assessment, then adjust if needed.

• You’re correcting the same error in another tax year
  Each year must be amended individually—do not submit one request covering multiple years.

• A small correction with no tax impact
  If the error does not change your refund or balance owing, CRA may not require a formal update (though it’s still good practice).