🇨🇦 Canada · 5 min read · Published 2026-09-07 · Updated 2026-09-07

Written by Jordan Reeves · Editorial review: automated source and figure checks (how we check this)

Sources last verified: 2026-09-07

How Do I Fix a Mistake on an Old Tax Return?

An adjustment request for an ordinary error, and the voluntary disclosures program where income went unreported. The difference matters, because disclosure offers relief from penalties and partial interest relief but only where the application is genuinely voluntary.

60-SECOND ANSWER

An adjustment request fixes ordinary errors; voluntary disclosure covers unreported income but only before the CRA makes contact.

The answer:: Request an adjustment for a missed credit or a wrong figure; use the disclosures program for unreported income or unfiled forms.
The trap:: Waiting until you are contacted. A disclosure is not voluntary once the Agency has initiated enforcement action on the matter.
The recommendation:: Deal with unreported foreign income promptly, because the reassessment period is extended where a form was not filed.

Jump to the detail ↓

Where the AI summary above gets this wrong

"You can just file an amended return to fix any tax mistake."

That's surface-true. Here's what it misses:

Adjustments cover ordinary errors — A missed receipt, a wrong figure or an unclaimed credit is corrected by an adjustment request, generally for the prior ten years.
Unreported income is different — Where income was not reported at all, the voluntary disclosures program is the route, with conditions and relief levels that vary.
Voluntariness is the gating condition — Relief is unavailable once the Agency has begun enforcement action relating to the matter, which is why timing decides everything.

→ See what unreported income costs at your rate

01 When an adjustment is enough

A missed medical receipt, a slip that arrived after filing, an unclaimed credit or a transposed figure is corrected with an adjustment request. It can generally be made for any of the previous ten calendar years, through the online account or on the prescribed form.

This is routine and carries no penalty implication. Interest applies to any additional tax owing from the original due date, which is the only cost of correcting an honest arithmetic mistake.

Source: Canadian income tax rates for individuals

02 When disclosure is the route

Where income was not reported at all, or a required form such as a foreign property return was never filed, the voluntary disclosures program is the mechanism. A successful application can provide relief from penalties and partial relief from interest.

The program distinguishes between categories of application, with less relief where the conduct was more serious. Unfiled foreign property reporting is a common trigger and carries its own extended reassessment period — the requirement is in reporting foreign property.

WORKED EXAMPLE · Try the numbers

Shows: what a given amount of additional taxable income costs you in tax at your marginal rate, and what you keep. Ignores: provincial surtaxes, credits that phase out with income, and any effect on income-tested benefits.

Amount ($)

Your marginal rate (%)

What you keep after tax

$6,700

At a 33% marginal rate, $10,000 costs $3,300 in tax and leaves $6,700.

Source: Canadian income tax rates for individuals

03 Why timing decides it

An application is not voluntary if the Agency has already initiated enforcement action relating to the taxpayer or the issue. A letter, a review or an audit closes the door, and information received from another country can close it without any contact at all.

That is the whole reason these applications are made promptly rather than considered at leisure. Once contact has been made, the ordinary objection process is what remains, and it is described in CRA reviews and notices of objection.

An application can be made on a no-names basis first in some circumstances, which lets the facts be described and the likely treatment discussed before the taxpayer is identified. Where the amounts are significant that step is worth taking, because it is the only point at which the question can be explored without committing. A successful application does not stop the Agency assessing the years in question; it limits penalties and part of the interest, and the tax itself remains fully payable.

Source: Leaving Canada (emigrants)

The thing that ends this option is rarely a letter. Information sharing between countries means an account abroad can surface without anyone contacting you first, and by the time the letter arrives the voluntary route has already closed.