What CRA actually does with an unmatched slip
Every T4, T5, T3, T4A and T5008 an issuer files goes into CRA's systems under your social insurance number, and months after your return is assessed, usually in the fall or winter, the matching program compares the two piles. When a slip on file does not appear on your return, one of two things arrives: a letter proposing to add the income and asking whether you agree, or a Notice of Reassessment that has simply added it. Neither is an audit. No one has reviewed your affairs or formed a view of you; a computer found a difference and the system is processing it.
That framing matters because it tells you what kind of response works. This is not a persuasion exercise; it is an arithmetic one. If the slip is genuinely yours and correct, the income was always taxable and the reassessment is simply the return you should have filed. If the slip is wrong, duplicated or not yours, the process has a lane for that too, covered below. Either way, ignoring the letter is the one move with no upside, because the reassessment proceeds without you and interest runs while you wait.
What it costs: interest always, penalties only sometimes
The certain cost is arrears interest: CRA charges it on the extra tax from the day the balance was originally due, at the prescribed rate for overdue amounts, which resets quarterly and compounds daily. Because matching happens months or more than a year after filing, the interest clock has been running the whole time, which is the best argument for paying promptly even if you intend to dispute details.
The penalty question turns on your history. A first missed slip generally brings no penalty, just the tax and interest. But the Income Tax Act carries a specific repeated-failure-to-report penalty: it can apply when you fail to report income of at least a few hundred dollars in one year and had done the same in any of the three preceding years. Where it applies, the penalty is calculated as the lesser of a percentage of the unreported amount and a portion of the understated tax after credit for what was withheld at source, a design that softens the blow where the slip already had tax deducted, and hits hardest where nothing was withheld. Separately, the gross negligence penalty exists for knowing or careless understatement; a genuinely overlooked slip that CRA caught by matching is not normally that territory.
The facts that change how serious this is:
- Whether this is your first missed slip or there is one in the previous three years
- Whether tax was withheld at source on the slip, as on most T4s
- The size of the unreported amount and the extra tax it produces
- Whether the slip is correct, or amended, duplicated or not yours
- Whether other years have the same gap CRA has not raised yet
What to do in the next two weeks
Start by pulling the slip itself from CRA My Account and checking it against your own records, because issuers file amended and occasionally duplicate slips, and the matching system is only as good as what was filed about you. If the slip is correct, agree, and pay the reassessed balance or arrange a payment plan; interest stops accruing only on what is paid. If CRA sent a proposal letter rather than a reassessment, respond within its deadline so the file closes on your terms.
Then look sideways at the years CRA has not mentioned. A slip missed once is often a slip missed by process, the same investment account, the same trust, the same side income, so check the prior returns for the same gap. Corrections you volunteer are handled differently from corrections CRA imposes: an ordinary missed year can be fixed with an adjustment through ReFILE or Change My Return, and where several years of unreported income exist that CRA has not touched, the Voluntary Disclosures Program can provide penalty relief and partial interest relief, but only while the disclosure is still voluntary. Once CRA has started matching a given year, that year is theirs to reassess; the surrounding years may still be yours to fix on better terms.
| Your situation | What CRA will likely do | Your move |
|---|---|---|
| First missed slip, slip is correct | Reassess with tax and arrears interest | Agree, pay or arrange, fix the intake process |
| Second miss within four years | Reassess and consider the repeated-failure penalty | Pay, then have the penalty math checked; relief requests exist |
| Slip is wrong, amended or not yours | Process the slip as filed unless challenged | Get the issuer to correct it; respond with documents; object if needed |
| Several years unreported, CRA silent so far | Matching will likely find them eventually | Consider a voluntary disclosure before CRA moves first |
If the slip is wrong, dispute it properly
A wrong slip is fixed through the issuer first and CRA second. Employers, banks and fund companies file amended slips routinely, so if the amount is wrong or the slip duplicates another, ask the issuer to amend it and tell CRA that is in motion; a corrected slip usually resolves the mismatch at the source. Where the issuer will not move or the disagreement is about whose income it is, respond to CRA with the documents that tell the story: statements, contracts, proof the income was reported elsewhere or belongs to someone else.
If a reassessment has already been issued and you disagree, the formal protection is a Notice of Objection, generally due within 90 days of the reassessment date, and preserving that deadline matters even while friendlier channels are still working. Interest continues to run on unpaid balances during a dispute, so on close calls it is often cheaper to pay the disputed amount and recover it with interest if you win. This is the same posture that serves you in heavier CRA mail, and the graduated playbook is laid out in what to do after receiving a CRA review letter and, for the rarer full audit, what to do after receiving a CRA audit notice.
Make sure it cannot happen twice
Because the repeated-failure penalty is triggered by a second miss within a four-year window, the cheapest tax planning available to you right now is process. The fix is a filing routine that reconciles your return against CRA's own records before it goes in: My Account lists the slips filed under your SIN, Auto-fill can pull them into the return, and a final cross-check catches the slip that arrived in February and was filed on the fridge. Late slips are a known trap, since T3s and amended slips can arrive after you have filed, so anyone with investment or trust income should diarize a post-season check.
The same discipline scales up for owners. A compliance calendar that tracks every slip source, filing deadline and instalment across you and the corporation is standard equipment in our engagements, and document retention is part of it: keep the records behind each return for six years from the end of the year they relate to, because that is the window in which CRA can ask. When we onboard a new client, reviewing the last few years of slips and returns against CRA's records is a deliberate first step, precisely because inherited gaps become repeated-failure penalties on our watch; if the gap traces back to work a prior accountant filed, your previous accountant made a tax error, what happens next covers who fixes what.
If the letter in front of you is more tangled than one slip, several years, a penalty already assessed, or a dispute worth fighting, this is what our CRA support work is for: we deal with CRA on your behalf, quantify the honest exposure, and file the corrections, objections or relief requests that fit. As a CPA firm handling CRA support and corporate compliance for Ontario owners, we would rather build you the calendar than the objection, but we do both, starting with a free 15-minute discovery call.
