How do I amend a T4 slip after it's filed, and do I need a new T4 Summary?
To amend a filed T4, send only the slips that change, with every box filled in. Online, file an amended return (report type code A) whose T4 Summary carries only those slips' totals. On paper, write AMENDED on each slip, mail one copy to the CRA with a letter, and skip the summary.
Which filing method you use decides what you send
The CRA expects an amended or cancelled slip when you've already filed and you know a box or code on it is wrong canada.ca. That includes a wrong dental code in T4 box 45, even though it changes no tax. Every method has the same core rule: include only the slips being corrected, and fill in every box on them, including the ones that were right the first time
canada.ca. What changes is the marking, the summary and where the explanation goes.
| Web Forms | Internet file transfer (XML) | Paper | |
|---|---|---|---|
| How you mark it | Return type Amended, slip type Amended | Report type code A on the summary and the slips | AMENDED written at the top of each slip |
| Amended T4 Summary | Yes, Web Forms builds it for you to review | Yes, totals of the amended slips only | No |
| Where the reason goes | Explanation for amendments box (1,250 characters) | Filer amendment note (1,309 characters) | A letter to your NVCC |
The character limits and the paper steps come from the CRA's T4 guide for 2025 canada.ca. Name the employee in the explanation when the reason applies to one slip. If you filed the original with Web Forms and saved it, you can import that file and pick Amended instead of keying every slip again
canada.ca. Online, you need a web access code, or you can sign in to My Business Account or Represent a Client without one
canada.ca.
When does the CRA say not to amend a T4?
Six situations look like amendments and aren't. In each one the CRA tells you not to send amended slips canada.ca.
| Situation | What to do instead |
|---|---|
| Only the employee's address changed | No amended slip |
| Your client's business name or address changed | Contact the CRA directly |
| You received a PIER report | Answer the PIER; the CRA prepares the amended slips |
| The original return hasn't been processed yet | Wait until it is |
| The slips were never sent | Prepare new slips, or initial the changes, and correct the summary |
| The client wants salary turned into dividends | Not allowed after the T4 is filed |
With a PIER, the CRA prepares two copies of each amended slip itself, one for you and one for the employee, and tells you not to send your own canada.ca. If you agree with the PIER, pay the exact amount by the deadline. If you don't, send it back with corrected figures within the 30 days.
The salary case is a hard stop. The CRA won't let a shareholder paid by salary retroactively convert salary to dividends, reduce the shareholder loan account with it, move the earnings to another person or split them with a spouse once the financial statements and the T4 are filed canada.ca. The source deductions on that salary still have to be remitted on time.
How do you fix two keying errors in a 12 slip XML return?
Your client filed 12 T4 slips by Internet file transfer. Two came out wrong: Ana's box 22 was keyed as $6,840 when payroll withheld $8,640, and Ben's box 14 was keyed as $45,500 when his earnings were $54,500. Payroll itself ran correctly, so only the slips are wrong.
| Ana | Ben | Amended summary | |
|---|---|---|---|
| Box 14, employment income | $50,000 (unchanged, still entered) | $54,500 (was $45,500) | Line 14: $50,000 + $54,500 = $104,500 |
| Box 22, income tax | $8,640 (was $6,840) | $7,900 (unchanged, still entered) | Line 22: $8,640 + $7,900 = $16,540 |
| Report type code | A | A | A |
The amended file holds two slips, not 12, and the summary carries the full corrected totals of those two slips canada.ca. Two mistakes are common here. Entering only the differences ($8,640 less $6,840 is $1,800; $54,500 less $45,500 is $9,000) is wrong, and so is resending all 12 slips with the year's grand totals. Every other line on the summary (CPP, EI and the rest) follows the same rule: the two slips' boxes added together.
Had the client filed on paper, you'd write AMENDED on both slips, give each employee two copies, mail one copy of each to the NVCC with a letter explaining the keying errors, and send no summary at all canada.ca. How the original summary fits together is in the T4 Summary.
How do you cancel, add or replace a T4 slip?
Cancelling looks like amending with one code changed. A missed slip goes in as a new original return online, and a replacement for a lost slip never goes to the CRA canada.ca.
| Action | Online | Paper |
|---|---|---|
| Cancel a slip | XML: code A on the summary, code C on the slip, all original data entered. Web Forms: Amended return, slip type Cancelled | CANCELLED at the top, all boxes completed, two copies to the employee, one to the NVCC with a letter |
| Add a slip you missed | File a new original return | ADDITIONAL at the top, one copy to the NVCC with a letter, no amended summary |
| Replace a lost slip | Nothing to file | DUPLICATE at the top, give it to the employee, keep a copy |
| Cancel the whole return | Online, or a request to your NVCC | Mail or fax to your NVCC, attention Employer Services |
A cancelled slip has to carry the data that was on the original, because the CRA rejects an empty one canada.ca. Additional slips filed after the due date may draw a penalty, and the CRA recalculates the late filing penalty and sends a new notice of assessment when T4 slips are added or cancelled
canada.ca. The penalty table is in the T4 slip deadline, and the two online channels are compared in filing T4 slips online.
What does the employee do if they already filed?
If the employee already filed with the old figures, they ask the CRA to change the return. They have to wait for the notice of assessment on the original return first, and only one change request can be open at a time canada.ca.
| Method | Years it covers | Typical processing time |
|---|---|---|
| Change my return in CRA My Account | 2016 and later | About 2 weeks |
| ReFILE through certified tax software | 2021 and later | About 2 weeks |
| Form T1-ADJ by mail | See the 10 year refund limit below | About 19 weeks |
Some requests take up to 35 weeks. The CRA won't issue a refund on a request made more than 10 calendar years after the end of the tax year canada.ca. Tell the employee which box changed and by how much, so the request matches the amended slip the CRA has on file.
Sources
Is there a deadline for filing an amended T4?
Do I have to redo the pension adjustment when I amend a T4?
Only if the PA changes by $250 or more, unless the employee or the CRA asks for it. When it does, report an amended PA for each affected year on an amended T4 canada.ca. The calculation itself is in the pension adjustment.
Can I amend a slip that went in on paper before the CRA processes it?
No. The CRA can't complete a paper amendment until the original return is processed, and it says not to send amended slips for a return it hasn't processed yet canada.ca. Wait for the processing, then amend.
The SIN on a slip is wrong. Is that an amendment?
Yes. The SIN is a box on the slip, and the CRA wants an amended slip whenever any box or code you filed is incorrect canada.ca. Complete every box on the amended slip, not just box 12. The boxes are listed in the T4 boxes explained.
General information for the tax year shown, not advice for a specific client. Confirm the facts before you file or remit.