How long does CRA have to reassess my income tax return?

The Income Tax Act is a federal statute that sets a "normal reassessment period." For most individuals and Canadian-controlled private corporations, CRA has three years from the mailing date of the original Notice of Assessment to reassess your return. For larger corporations the period is four years, and for transactions with non-arm's-length non-residents it can be longer.

After the normal period expires, a tax year is generally considered statute-barred and CRA cannot change it — unless an exception applies. The main exception is misrepresentation: if you made a misrepresentation in your return that was attributable to neglect, carelessness, wilful default, or fraud, CRA can go back as far as it needs to. There is no time limit on reassessing fraud.

In practice this means a sloppy or incomplete return carries long-term risk even after the three-year window closes. CRA can also reassess beyond the normal period if you waive it in writing, which auditors sometimes request — never sign a waiver without advice. If you filed a request for loss carryback or similar adjustment, the resulting reassessment has its own timing rules.