HST/GST Audit Defense for Canadian Small Business: What the CRA Actually Checks

A GST/HST audit is not a smaller version of an income tax audit. The money at stake was never yours. You collected it as an agent of the Crown, and the auditor’s starting assumption is that it should be remitted unless you can show otherwise. That single difference explains why these reviews feel less negotiable than an income tax review of the same business, and why the defence is almost entirely documentary.

The good news is that the failure points are narrow and predictable. Most assessments I see come from four or five recurring errors, none of which is about aggressive planning.

What actually brings a GST/HST review

A refund position. A return claiming net tax refundable gets more attention than one remitting, for the obvious reason. This is not an accusation. It is triage.

Input tax credits out of proportion to sales. The CRA has a good sense of the ITC-to-revenue ratio for your industry. A number well outside the band invites the question of whether personal purchases, exempt-activity inputs or ineligible items are in the pool.

Sales on the GST/HST returns that do not tie to the income tax return. Twelve months of GST/HST returns should reconcile to the revenue reported on your T2 or T2125, with explainable differences for exempt and zero-rated supplies. When they do not, the mismatch is mechanical and it is found automatically.

Late registration. You stop being a small supplier the day you exceed $30,000 in a single calendar quarter, and the registration rules make your effective date of registration no later than the day of the supply that put you over. You must charge tax on that very sale, and you have 29 days to register. Businesses that register the following year and start charging then own an uncollected liability for the gap. The thresholds and the alternative four-consecutive-quarter test are in GST/HST registration for small business.

Misclassified supplies. Treating a taxable supply as exempt is the expensive version of this error, because the tax was never collected and now comes out of margin. See exempt vs zero-rated.

Wrong rate on out-of-province sales. Ontario HST is 13%, and the correct rate depends on the place of supply rather than where your office is. The rules are set out in place of supply.

Nil returns, or a run of them, from a registrant with visible activity.

Closing or deregistering, which triggers the change-in-use and deemed disposition rules on any property the business still holds.

The documentary requirement is the whole ballgame

Almost every ITC denial I have seen was denied on paperwork, not on principle. The business genuinely incurred the cost, genuinely used it commercially, and still lost the credit.

The rules step up in three tiers by the size of the invoice. At every tier, the item most often missing is the supplier’s GST/HST registration number. Above the top tier you also need the recipient’s name and the terms of payment. The current tiers and their dollar thresholds are set out in the CRA’s Memorandum 8-4 and in RC4022; check them there rather than relying on figures quoted in an article, because they have moved.

Verifying a supplier’s registration number in the CRA’s public GST/HST Registry takes under a minute and is the single highest-return control a small business can add. If the supplier is not registered, the tax they charged is not recoverable by you, and the CRA will not fund your loss.

The deadlines that bind

The filing deadlines are on the CRA’s reporting requirements and deadlines page. The 90-day objection window is the one people lose. It runs from the date on the notice, not from the day you opened the envelope.

When the letter arrives

GST/HST letter received
│
├─ Is it a request for specific documents on one period?
│   └─ Yes ──► Send exactly what was asked, by the stated date.
│              Do not volunteer other periods.
│
├─ Is it notice of a full audit, with a period range?
│   │
│   ├─ Are your ITC source documents complete for those periods?
│   │   ├─ Yes ──► Reconcile returns to the books first,
│   │   │          then hand over a clean, indexed package.
│   │   └─ No ───► Quantify the exposure before the auditor does.
│   │              Get representation.
│   │
│   └─ Do you already know about unreported tax collected?
│       └─ Yes ──► The Voluntary Disclosures Program closes the
│                  moment the CRA contacts you about it. This
│                  letter may already have closed it. Get advice
│                  the same week.
│
└─ Is it a notice of assessment you disagree with?
    └─ Diarize 90 days from the date on the notice.
       File the objection before the window closes.

Conduct during the audit

Reconcile before you produce anything. If your GST/HST returns do not agree with your own books, you want to know that first, and you want the explanation ready. Discovering it alongside the auditor is a bad way to discover it.

Answer the question asked. Producing three extra years of records to appear cooperative expands the scope. That is not evasiveness; it is ordinary scope management, and the CRA’s own overview of what to expect in an audit sets out what they are entitled to.

Watch for sampling and projection. GST/HST auditors frequently test a sample period and extrapolate the error rate across the whole audit period. A single badly documented month can become a four-year assessment. If a projection is proposed, ask how the sample was chosen and whether it is representative. That is a legitimate and often successful line of argument.

Keep it in writing. Confirm phone calls by email the same day. What was agreed on a call is worth nothing at the objection stage unless someone wrote it down.

Separate the accounts. The largest driver of audit pain in a small business is a commingled bank account, because every transaction then needs an explanation. The monthly discipline that prevents this is described in the monthly close.

If the assessment is wrong

An auditor’s conclusion is a position, not a verdict. File a notice of objection within 90 days; the process is described in the CRA’s Memorandum 31 and the practical side in objecting to a reassessment. Appeals officers are independent of the audit function, and well-documented positions are frequently sustained there.

Penalties and interest are a separate question from the tax. Where the failure came from circumstances beyond your control or from a CRA error or delay, a taxpayer relief request can address the interest and penalties even where the tax itself stands.

If you know about a problem before the CRA does, the Voluntary Disclosures Program exists for exactly that situation. The disclosure must be genuinely voluntary. Once contact has been made about the issue, the door is shut.

The prevention that actually works

Reconcile GST/HST collected to revenue once a year, before the income tax return is filed. Verify supplier registration numbers on any recurring or material vendor. Keep the invoice, not the statement. File on time even when you cannot pay, because the failure-to-file consequences and the failure-to-pay consequences are different problems. Nothing here is clever, and it is most of the difference between a two-week audit and a four-year assessment.

If a GST/HST letter has arrived and you are not sure what it is asking or what it is exposing, send it over before you reply. The first response sets the scope for everything that follows.