Fixing a mistake in your (already filed) tax return

May 25, 2021by AB

For the majority of Canadians, the due date for filing of an individual tax return for the 2020 tax year was Friday April 30, 2021. (Self-employed Canadians and their spouses have until Tuesday June 15, 2021 to get that return filed.) In the best of all possible worlds, the taxpayer, or his or her representative, will have prepared a return that is complete and correct, and filed it on time, and the Canada Revenue Agency (CRA) will issue a Notice of Assessment indicating that the return is “assessed as filed”, meaning that the CRA agrees with the information filed and tax result obtained by the taxpayer. While that’s the outcome everyone is hoping for, it’s a result which can go “off the rails” in any number of ways.

By April 26, 2021, just over 20 million individual income tax returns for the 2020 tax year had been filed with the CRA. And, inevitably, some of those returns contain errors or omissions that must be corrected.

Over 93% of the returns which have already been filed for the 2020 tax year were filed through online filing methods, meaning that they were prepared using tax return preparation software. The use of such software significantly reduces the chance of making a clerical or arithmetic error, like entering an amount on the wrong line or adding a column of figures incorrectly. However, no matter how good the software, it can work only with the information that is provided to it. Sometimes taxpayers prepare and file a return, only to later receive a tax information slip that should have been included on that return. It’s also easy to make an inputting error when transposing figures from an information slip (a T4 from one’s employer, for instance) into the software, such that $58,479 in income becomes $54,879. Whatever the cause, where the figures input are incorrect or information is missing, those errors or omissions will be reflected in the final (incorrect) result produced by the software.

When the error or omission is discovered in a return which has already been filed, the question which immediately arises is how to make things right. The first impulse of many taxpayers is to file another return, in which the complete and correct information is provided, but that’s not the right answer. There are, however, several ways in which a mistake or omission on an already filed tax return can be corrected, including online options.

Since 2018, taxpayers who file their tax returns online, whether through NETFILE or EFILE, have been able to notify the CRA of an error or omission in an already filed return electronically by using the CRA’s ReFILE service. That service, which can be found at, allows taxpayers to make corrections to an already filed return online, on the CRA website.

Essentially, taxpayers whose returns have been filed online (through NETFILE or EFILE) can make a correction using the same tax return preparation software that was used to prepare the return. Those taxpayers who used NETFILE to file their return can file an adjustment to a return filed for the 2017, 2018, 2019, and 2020 tax years. Where the return was filed using EFILE, the EFILE service provider can similarly file adjustments for returns filed for the 2017, 2018, 2019 or 2020 tax years.

There are limits to the ReFILE service. Regardless of who is using the service (i.e., the taxpayer or an EFILE service provider) the online system will accept a maximum of 9 adjustments to a single return, and ReFILE cannot be used to make changes to personal information, like the taxpayer’s address or direct deposit details. There are also some types of tax matters which cannot be handled through ReFILE, like applying for a disability tax credit or child and family benefits.

It’s also possible to make a change or correction to a return using the CRA’s “My Account” service (through the “Change My Return” feature), but that choice is available only to taxpayers who have already become registered for My Account. Taxpayers who opt to become registered for My Account, in order to access the broader options available through Change My Return should be aware that that registration process takes a few weeks, in order to satisfy the CRA’s security measures.

While using the CRA’s online services, whether through ReFILE or My Account is certainly the fastest way to make a correction on an already filed return, taxpayers who don’t wish to use an online method do still have a paper option. The paper form to be used is Form T1-ADJ E (20), which can be found on the CRA website at T1-ADJ T1 Adjustment Request – Those who are unable to print the form off the website can order a copy to be sent to them by mail by calling the CRA’s individual income tax enquiries line at 1-800-959-8281. There is no limit to the number of changes or corrections which can be made using Form T1-ADJ E (20).

The use of the actual T1-ADJ (20) isn’t mandatory — it’s also possible to file an adjustment request by sending a letter to the CRA — but using the prescribed form has two benefits. First, it makes clear to the CRA that an adjustment is being requested. Second, filling out the form will ensure that the CRA is provided with all the information needed to process the requested adjustment. And, whether the request is made using the T1 Adjustment form or by letter, it’s necessary to include any relevant documents — the information slip summarizing the income not reported, or the receipt for an expense inadvertently not claimed.

Hard copy of a T1-ADJ(20) (or a letter) is filed by sending the completed document to the appropriate Tax Center, which is the one with which the tax return was originally filed. A listing of Tax Centres and their addresses can be found on reverse of the TD-ADJ (20) form. A taxpayer who isn’t sure any more which Tax Centre his or her return was filed with can go to on the CRA website and select his or her location from the drop-down found there. The address for the correct Tax Centre will then be provided.

Where a taxpayer discovers an error or omission in a return already filed, the impulse is to correct that mistake as soon as possible. However, no matter which method is used to make the correction — ReFILE, My Account, or the filing of a T1-ADJ in hard copy, it’s necessary to wait until the Notice of Assessment for the return already filed is received. Corrections to a return submitted prior to the time that return is assessed simply can’t be processed by the Agency.

Once the Notice of Assessment is received, and an adjustment request is made, it will take at least a few weeks, usually longer, before the CRA responds. The CRA’s goal is to respond to such requests that are submitted online within about two weeks, while those which come in by mail currently take about ten to twelve weeks. Not unexpectedly, all requests which are submitted during the CRA’s peak return processing period between March and July will take longer.

Sometimes the CRA will contact the taxpayer, even before a return is assessed, to request further information, clarification, or documentation of deductions or credits claimed (for example, receipts documenting medical expenses claimed, or child care costs). Whatever the nature of the request, the best course of action is to respond promptly, and to provide the requested documents or information. The CRA can assess only on the basis of the information with which it is provided, and it is the taxpayer’s responsibility to provide support for any deduction or credit claims made. Where a request for information or supporting documentation for a claimed deduction or credit is ignored by the taxpayer, the assessment will proceed on the basis that such support does not exist. Providing the requested information or supporting documentation can usually resolve the question to the CRA’s satisfaction, and its assessment of the taxpayer’s return can then be completed.


The information presented is only of a general nature, may omit many details and special rules, is current only as of its published date, and accordingly cannot be regarded as legal or tax advice. Please contact our office for more information on this subject and how it pertains to your specific tax or financial situation.