In most cases, the CRA will explain how they calculated your tax refund or balance owing, and you can find this information on your Notice of Assessment (NOA), under the heading Explanation of changes and other important information. Compare the line numbers on your NOA and their corresponding values with those entered into TurboTax.

The reasons for discrepancies may vary, and can range from very simple (typo or data entry error, forgotten slip, receipt, amount, etc) to complex (carry-forward amounts not included, accounting errors, etc).