What to Do If You Make a Mistake on Your Tax Return in Canada

Woman hand working with calculator, business document and laptop computer notebook,
krisanapong detraphiphat / Getty Images

It’s always a satisfying moment when you hit the send button and efile your Canadian income tax—unless it’s one of those times when you realize afterward that you’ve made a mistake and shouldn’t have hit the button quite so quickly.

You’ve found some more receipts or used the wrong class when you were figuring your capital cost allowance, for instance. Or, you used the wrong dates for your medical deductions.

If you make a mistake on your tax return, don’t panic. The Canada Revenue Agency (CRA) is not going to rush out to your home and take you into tax custody. Instead, they have a procedure to follow so you can change your tax return after filing and fix the mistake you’ve made.

First, wait for your notice of assessment to arrive because there’s nothing you can do until it has. Once you have it, you’ll be able to request changes to your return in a variety of ways, depending on whether it is a T1 (individual) return or a T2 (corporate) return.

Requesting to Change Your T1

If you are requesting a change to a T1 income tax return, you can do it online or by mail in one of these three ways:

  1. Use the change my return option found in My Account, one of the CRA’s secure online services. You must sign up for My Account.
  2. Send a completed T1 Adjustment Request form (T1-ADJ) to your tax center.
  3. Send a signed letter to your tax center asking for an adjustment to your return.

If you are requesting a change via mail, you need to be sure you include all the supporting documents related to the change(s) you are requesting, including those from your original income tax assessment if you haven't already submitted them to the CRA. You also need to submit:

  • the details of your request, including the years of the tax, returns to be changed;
  • your social insurance number;
  • your address; and
  • a phone number where you can be reached during the day.

Online or by mail, you can request a change to any return for the previous nine years as well as requesting a change to your tax return for the current year.

If you are asking for changes to be made to tax returns for different years, you need to prepare separate forms or letters for each change and submit the change requests for each year separately.

T1 Response Time

Once the CRA has reviewed your request for a change to your T1 form, it will let you know whether they’re going to allow the change or not by sending you a notice of reassessment showing the changes they have made to your income tax return or a letter explaining why they didn’t make the changes you requested.

Expect to wait two weeks if you’ve requested a change online or eight weeks if you’ve requested a change by mail, according to the CRA website.

The CRA cautions that it might take additional time for your request to be processed if it needs to contact you for more information or documentation or if you send in your request to make a change to your income tax return in spring or early summer.

Requesting to Change Your T2

As is the case with a T1 return, you can't change your T2 tax return after filing until your corporation receives its notice of assessment. Once that's happened, requests to make changes to Canadian corporate income tax returns also can be made electronically or by mail.

Make your request electronically by using commercial Canadian tax software or by sending your amended T2 income tax return in barcode format to the CRA. You also can write a letter and mail it to the appropriate tax center. Make sure your letter includes:

  • the name of the corporation;
  • the corporation's business number (BN);
  • the corporation's tax year; and
  • any details that apply, including revised financial statements and revised schedules.

If the change you want to make involves asking to carry back a loss or tax credit to a previous tax year, you will need to file whichever of the following schedules apply:

Past Years

How far back you can go to change T2 forms depends on what type of corporation you have and what kind of reassessment is being asked for. The CRA’s normal reassessment period for a T2 return is within three years of the date it mailed the original notice of assessment for the tax year if the corporation was a Canadian-controlled private corporation (CCPC) at the end of the tax year or within four years of the date it mailed the original notice of assessment for the tax year if the corporation wasn’t a CCPC. However, extensions are possible.

Once the CRA has received your request for a reassessment of your corporate income tax return, it will review your request, then send you a notice of reassessment showing the changes it has made to your income tax return or a letter explaining why it didn’t make the changes you requested.

T2 Response Time

It's difficult to say how long the process will take; the CRA does not post any specific timelines for reassessments of T2 tax returns. The time frame for reassessment depends on the type of reassessment you’re requesting, whether your request needs more review, or the CRA needs to contact you or your authorized representative for more information or documentation and whether you’ve sent your request in late summer or fall, which lengthens the process.