Who this is for
Anyone who filed and then found a slip in a drawer or got a late T4A. Anyone who forgot an RRSP receipt or a donation, or claimed something they should not have. It also covers older years. If you never filed the year at all, that is a different situation. See our guide on unfiled returns.
One thing most people do not realize
You can go back ten calendar years, but the CRA will not accept any change until it has assessed the original return. Filing a second return for the same year does not work; it causes delays. Wait for the Notice of Assessment, then request the change.
First, wait for the Notice of Assessment
The CRA will not accept a change until it has assessed the return you already filed. Wait for the Notice of Assessment. Then request the change. Do not send a second return for the same year. That causes confusion and delays.
Three ways to request a change
Online in CRA My Account. Use the “Change my return” service. The CRA’s stated processing time is about two weeks.
Through tax software. Certified software can send the change with a service called ReFILE. We do this for returns we prepared. Also about two weeks.
On paper. Fill in Form T1-ADJ and mail it with your supporting documents. The CRA’s stated processing time is about 19 weeks. Use paper only when online is not possible.
How far back you can go
You can request a change for any of the past 10 calendar years. The CRA will not issue a refund for a year older than that. If you found something from several years ago, it is still worth checking.
What happens next
The CRA reviews the request and sends one of three things. A Notice of Reassessment with the change. A reassessment with only part of the change and an explanation. Or a letter saying why it was refused. If the change means a refund, it comes the same way your refunds normally do. If it means you owe more, interest is charged from the original due date, so sooner is better.
What to bring
- The year that needs changing
- The slip, receipt or document that was missed, or a note of what was claimed by mistake
- Your Notice of Assessment for that year
- Your CRA My Account login if you want us to use it with you, or a signed authorization so we can act for you
Small things that are still worth fixing
A missed RRSP receipt. A medical expense that pushes you over the threshold. A tuition amount that could be carried forward. A T4 from a short job that the CRA will match anyway. Fixing it yourself is almost always better than waiting for the CRA to find it. Interest and a possible penalty run from the original date either way.
Official sources
This guide is general information, not advice about your situation. It reflects the rules for the 2025 and 2026 tax years. It has not yet been reviewed by a practitioner. The information was checked against the official sources listed above on the date shown. Rules change. Check the official sources above or ask us. How we prepare these guides.