Tax payers are often faced with the challenge of correcting their taxes after they have filed. In my experience, filing too early without all available slips, or forgetting the details of receipts are the main reasons
Common missing information are RRSP slips, investment slips, donation receipts medical receipts, and home office expenses.
I wanted to point out that tax records (e.g., T4s, T3s, T4a, etc.) are not always available on CRAs My Account especially in February or March, so don’t be over reliant on this approach to get your slips. Similarly, these are common mistake made by tax preparers or tax volunteer who relies solely on auto fill.
Remember, the onus is on the tax payers to gather all their documents and have it available for filing.
Regardless, if you are face with this situation you can make changes. This can be done though ReFILE or Change my return (CMR) (this is a secure My Account service that allows you to make an online adjustment for the 10 previous calendar years ) or you can mail.
It is critical to mention that your return must be assessed before you can amend and Refile. Consult your tax advisor.
Normally, you can only request a change to a return for a tax year ending in any of the 10 previous calendar years. For example, a request made in 2021 must relate to the 2011 or a later tax year to be considered. (as per CRA). Individuals (NETFILE users) can use ReFILE to send adjustments for 2020, 2019, 2018 and 2017 returns.
Other lesser errors such as marital status, address, direct deposit and email address can be changed in My Account. Do not use Refile for these.
Some consultants or businesses may charge a ReFILE fee or change fee so be prepared make another payment or have these discussions up front.