The short version
- A notice of reassessment means CRA changed a return it had already assessed. Usually there's a bill attached.
- Find the one line that changed in the “explanation of changes.” That tells you what kind of problem you have.
- Income tax objection deadline: the later of 90 days after the notice date or one year after that return's filing due date. GST/HST: 90 days, full stop.
- Interest runs daily on the balance, including the part you dispute. Pay what you agree with now.
- If CRA only needed a receipt, send it. If CRA got the facts or rules wrong, file a notice of objection.
Notice of Reassessment: What to Do in the First 30 Days
A notice of reassessment usually shows up in the fall, long after you've spent the refund and forgotten what was on the return. Here's what to do, in the order that saves the most money and the most grief.
First, the honest part. Most reassessments aren't CRA calling you a crook. They come from computer matching (a slip CRA has that your return didn't), a review where the receipts didn't arrive in time, or a claim that didn't fit the rules. Many are fixed with one envelope of paper. Some aren't, and those are the ones where the deadline matters.
Step 1: Find the One Line That Changed
Skip the totals and go to the explanation of changes. It says which line CRA changed and why, in a sentence or two. “We disallowed your moving expenses because you didn't provide supporting documents” is a very different problem from “We added employment income of $8,450 from a T4 slip.”
If the wording is hard to follow, the tax document analyzer explains it in plain English. Upload the PDF from My Account or a photo, and cover your SIN first.
Step 2: Write Down Your Deadline. Today.
For an individual's income tax, you can object until the later of:
- 90 days after the date printed on the notice, or
- one year after the filing due date of that return (April 30 of the following year, or June 15 if you or your spouse had self-employment income).
For a reassessment of an older year, the 90 days usually wins, and 90 days goes faster than you think. The objection deadline calculator works it out from the date on your notice. Missed it? You can ask for an extension within one year after the deadline, with a reason.
Step 3: Decide If CRA Is Actually Wrong
Be honest with yourself here. It's cheaper than being honest with an appeals officer later.
- CRA is right. You forgot a T4 or claimed something you shouldn't have. Pay it and move on. Interest runs daily, so paying fast is the cheapest fix. Our page on missing T4 slips explains how matching works.
- CRA just didn't see your proof. You have the receipts, you just didn't send them in time. Often the fastest fix isn't an objection: send the documents through Submit documents in My Account, or call the number on the notice and ask how they want them. If your deadline is close, file an objection too, to protect your rights.
- CRA got the facts or the rules wrong. That's what a notice of objection is for.
Not sure which of the three it is?
Upload the notice. The Tax Document Analyzer reads the explanation of changes, tells you which line changed and why, and gives you the objection deadline.
Step 4: Pay What You Agree With
Interest keeps running on everything you owe, including the part you dispute. For income tax, CRA generally won't take collection action on the disputed amount while your objection is open, but interest still adds up. Paying the disputed part too stops the interest clock; if you win, CRA pays it back with interest. Can't pay at all? Call and ask for a payment arrangement before collections calls you. See CRA tax problems.
Step 5: File the Objection Properly
An objection is free and doesn't need a lawyer (the full guide is on CRA objection). File it online in My Account (“Register my formal dispute”) or on form T400A by mail. What wins is a clear statement:
- What you disagree with, line by line.
- Why CRA is wrong: the facts, and the rule if you know it.
- What the right amount should be.
- What proof you have, attached or offered.
Stick to facts. An appeals officer who wasn't part of the original decision reads it, and “I've always paid my taxes” doesn't move anyone. “My new home is 9 km from the office; the old one was 61 km away; the lease and my employer's letter are attached” does.
How long it takes: CRA's 2026-27 goal is to resolve low-complexity objections within 180 days and medium-complexity ones within 365 days. If you still disagree after that, the next step is the Tax Court of Canada.
Disagree with CRA? File the objection properly
The Objection Pack reads your notice, works out your deadline, drafts your statement of facts and fills in form T400A for you to sign.
Why CRA Can Still Change an Old Return
CRA can generally reassess an individual's return within three years of the date on the original notice of assessment. Longer in some cases: misrepresentation through carelessness or fraud has no time limit, and some items, such as loss carrybacks, get extra time. If the reassessment came because you asked for a change yourself, it isn't a problem, just paperwork; see how to change your tax return.
When to Get a Professional
Get help before you file the objection if the amount is large (say over $10,000), if CRA assessed gross negligence penalties, if the issue is residency, a business or income CRA says you hid, or if it's part of a wider audit. A tax lawyer or an accountant who handles disputes is worth the fee at that point. Find the right tax help explains who does what.
The Five Rules
- Read the explanation of changes, not the total.
- Write the objection deadline on the calendar.
- Pay what you agree with right away.
- Send documents if that's all CRA was missing.
- Object in writing, with facts and proof, before the deadline.
Don't want a repeat next year? Return Check compares your return with your slips and flags the claims CRA adjusts most, before you file.
Reassessment Questions
What is a notice of reassessment?
A notice from CRA saying it has changed a tax return it already assessed, usually after matching a slip, completing a review, or processing a change you requested. It shows what changed, why, and any new balance or refund.
How long do I have to object to a reassessment?
For individual income tax, the later of 90 days after the date on the notice or one year after the filing due date of that return. For GST/HST, 90 days. You can ask for an extension within one year after the deadline.
Do I have to pay while my objection is being reviewed?
For income tax, CRA generally does not collect the disputed amount while an objection is open, but interest keeps accumulating. Paying stops the interest, and CRA refunds it with interest if you win.
How long can CRA go back and reassess my return?
Generally three years from the date of the original notice of assessment for individuals, longer in some cases, and with no limit for misrepresentation due to carelessness, neglect or fraud.
Should I send documents or file an objection?
If CRA only lacked receipts, sending them through Submit documents in My Account is often faster. If CRA misread the facts or the rules, or your deadline is close, file a notice of objection.
Sources: CRA, P148 Resolving your dispute; Service Standards 2026-27; Common adjustments. Checked October 2026.
Last reviewed October 5, 2026 against CRA and Government of Canada sources. How we check our facts.