A notice of reassessment is the formal Canada Revenue Agency document that changes a prior notice of assessment for a tax year. It restates the tax, interest, and penalties owing — usually increasing them after an audit, but sometimes decreasing them in response to an amendment or refund claim.
A reassessment starts two clocks. The first is the deadline to file a notice of objection. The second is the path to a Tax Court appeal, which generally requires a valid objection first. The reassessment supersedes the prior assessment, so the taxpayer's liability is set by the most recent reassessment unless it is overturned on objection or appeal. The objection deadline is statutory and missing it is often fatal to a dispute.