The Canada Revenue Agency published guidance explaining how taxpayers can request changes after filing a return.
CRA said taxpayers may need to correct a return if they forgot to claim a deduction, omitted income, entered an amount incorrectly, or received new tax information after filing.
The change process can affect tax payable, refunds, benefit entitlement, credits, and future CRA correspondence. A reassessment can increase a refund, reduce a balance, create a new amount owing, or change income-tested benefits.
CRA said online requests can be faster than paper requests and can lead to a notice of reassessment and any related refund sooner.
For online requests, supporting documents are generally needed only if CRA contacts the taxpayer after the request is submitted. That differs from some paper processes, where documents may need to be sent with the request.
The guidance also matters for timing. A taxpayer should normally wait until receiving a notice of assessment before requesting a change, because CRA needs the original return to be processed before it can reassess the changed item.
Filing is not always the end of the process. If a return is wrong, correcting it through CRA channels is usually better than leaving the error to affect later benefits, credits, or compliance reviews.