What if I found a mistake after filing my return to CRA?

After your return has been filed with errors, it is possible that CRA could correct some or all errors for you. You can check your Notice of Assessment from CRA. If the errors have not been corrected by CRA, you have the following options to change your return:

1. File a paper T1-ADJ form; This option is slow (up to 8 weeks), however you can correct all kinds of mistakes using this form.
2. Make changes with your CRA "My Account". This process is online and is fast.
3. For 2015 and later tax years, you can use our ReFile service to change your return. At the time of this writing, CRA has enabled "ReFile" service for EFILE only, which means you cannot do it by yourself unless you register an EFILE number and purchase an eFILE product. We charge $20 to do it for you and it involves authorization/paperwork.

If you don't have many "raw" numbers (vs. calculated numbers) to change, option 1) and 2) are good enough. You only need to list the "raw" numbers that have been changed, like "add line 101 - employment income by $1,000", and CRA will recalculate the return.

Option 2) and 3) is fast, however, you might not be able to correct all types of errors, you can find the limitation on CRA website.

Here is CRA guide on How to change your return.

When you file a original return, CRA will take both original number and calculated numbers from the Netfile/EFile return. CRA does calculate by itself, however, as long as the difference is tiny (like below $2), CRA will use our calculated results so you will get what you see exactly in the software.

On the other hand, when you re-file a return, it works the same way as when you make changes through T1ADJ form or using CRA "My Account", CRA will only take a few original (as opposed to calculated) changed numbers, and recalculate your return. Due to CRA rounds up most lines to dollar only part, the final number might not match exactly. The difference usually is within a dollar but could be higher (never seen more than $3).