Canadian personal-return mechanics; examples assume all other adjustments are zero, not a particular income or tax year.
A refund generally arises when amounts credited to your return, including tax already paid and applicable refundable credits, exceed the final amount payable. Payroll withholding is a payment toward the eventual calculation, not a guarantee that the calculation will end at zero.
Withholding and final liability answer different questions
Your employer deducts income tax during the year. Your return reconciles annual income, deductions and credits using your complete facts. Multiple jobs, a change in work pattern or claims not reflected in payroll can leave a difference. A refund is not proof that the employer or taxpayer made a mistake.
Sources: CRA — T4 slip guide; CRA — Federal income tax and benefit information for 2025
Example: one tax bill, two payment histories
Assume final tax payable of $9,000, no refundable credits or other adjustments, and $10,000 withheld. The result is a $1,000 overpayment. With the same $9,000 liability but only $8,000 paid, the person owes $1,000 instead.
The size of the refund therefore does not tell you how much tax the person paid overall. Both examples have the same final liability. Receiving a bigger refund can simply mean more money was withheld earlier.
How a donation might change the balance
An eligible, usable non-refundable donation credit can lower the relevant tax payable. When payments are unchanged, that can increase an overpayment or reduce a balance owing. But if there is no applicable tax left to reduce, the credit cannot create negative tax. A gift does not guarantee a refund.
Sources: CRA — Gifts and Income Tax 2025
What to compare when a result surprises you
Compare actual withholding with the final return, not a refund from a different year in isolation. The simplified estimator requires tax deducted because it cannot infer your payment history.
- Add Box 22 across the relevant T4s.
- Check omitted income and claim changes.
- Review the notice of assessment for adjustments.
- Use complete filing software or qualified help for instalments, business income and complex credits.
Sources: CRA — Federal income tax and benefit information for 2025