While it can be a frustrating experience, it is fairly common for the Canada Revenue Agency (CRA) to make a tax return assessment that is different from yours.
The CRA collects and maintains your tax information, and they may already have some of your tax slips for the current year (for example, T4 slips submitted to the CRA by your employer,) as well as other tax-related information from previous years (such as carry-forward amounts, RRSP limits, etc.). When filing your taxes, the CRA considers all of this information in totality in making their assessment.
The reasons for these 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).
For more information, please see our FAQ TurboTax link as Why is the refund or balance owing on my Notice of Assessment different from what TurboTax calculate...
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