CRA sends three kinds of letters that all feel like the same nightmare. They're not. A review letter is routine paperwork. A reassessment is a number changing. An audit is the rare deep dive most Canadians never see. This guide explains how to tell them apart and what each actually requires.

The one-line difference

• Review letter: "Please send us receipts for line X." Routine.
• Reassessment: "We changed your numbers. Here's the new bottom line." Concrete.
• Audit: "We're examining your books. Make them available." Serious.

Review letter (the most common by far)

CRA sends roughly 3 million review letters per year. Most Canadians get one at some point, and most never get one again. Reviews fall into two streams:

1. Pre-assessment review — CRA holds your return before issuing the NOA, asks for documents, then issues the NOA. Usually adds 4–8 weeks to your refund timeline.
2. Post-assessment review — CRA already issued your NOA, then comes back later asking for backup. Either confirms your claim (no change) or triggers a reassessment.

Common review triggers:

• Medical expenses over a few thousand dollars
• Charitable donations over $1,000 or to a less-known charity
• Moving expenses
• Child care expenses (form T778)
• Employment expenses with a T2200 (especially home office)
• Business or rental losses
• Any first-year claim of a credit you've never claimed before

How to respond

1. Read the letter — it lists the exact line CRA wants documents for, and a deadline (usually 30 days)
2. Pull receipts, T-slips, or supporting forms for that line
3. Upload through CRA My Account → Submit documents → Reference the case number on your letter
4. Or mail/fax to the address on the letter

If your documents check out, you'll get a one-page "review concluded" letter and that's the end of it. No reassessment, no further contact.

Reassessment

A reassessment is a follow-up NOA that changes the numbers on a return CRA already assessed. It's a document, not a process. The format is identical to your original NOA, with one extra section: "Explanation of changes" listing what CRA changed and why.

Reassessments often follow a review letter — if the documents you sent didn't satisfy CRA, they reassess to remove the disallowed claim. They can also happen without any prior review (T-slip mismatch, post-filing data correction, or in response to your own T1 adjustment request).

Full breakdown in our reassessment vs assessment guide. Disputing one is covered in how to dispute a CRA NOA.

Audit (rare and serious)

Audits are conducted by CRA's Audit Division, not by the assessment teams. They're rare for individual taxpayers — under 1% of T1 returns are audited in any given year, and most of those audits are limited-scope reviews of self-employment income.

The audit letter is unmistakable. It will:

• Use the word "audit" in the subject line
• Name a specific CRA auditor with their phone number
• List the tax years being audited (usually 2–4 years)
• Ask for access to your books, records, and bank statements
• Often request an in-person or video meeting

Common triggers: large self-employment losses, repeated business losses (CRA's "personal endeavour" test), large GST/HST refunds claimed by small businesses, real estate flips, and crypto activity that doesn't match your reported income.

What to do if you're audited

1. Don't panic, don't respond same-day. The auditor will give you 30 days to provide documents. Use the time to organize.
2. Hire an accountant or tax lawyer. An audit is the one CRA process where professional representation usually pays for itself.
3. Don't volunteer information beyond what's asked. Cooperate, but don't expand the scope of the audit unprompted.
4. Use your right to representation — sign form T1013/AUT-01 to authorize the accountant or lawyer to deal with CRA on your behalf.

Quick comparison table

Bottom line

Identify which letter you got — the type is named at the top — and respond proportionally. A review letter is paperwork. A reassessment is a number you can dispute on a 90-day clock. An audit is the one to actually worry about, and the one where hiring a tax professional is usually the right call. Don't conflate them, and don't ignore any of them.

Related reading: NOA line-by-line guide, reassessment vs assessment, how to dispute a CRA NOA.

Sources: CRA — Your tax return was selected for review, CRA — Audits.