A GST/HST audit rarely begins with a phone call. It begins quietly, months earlier, when an automated CRA matching program compares the taxable supplies reported on a business's GST/HST return against the revenue reported on its corresponding income tax filing, and finds a gap large enough to warrant a closer look[1]. By the time a Notice of Audit actually arrives, the CRA's systems have often already cross-matched supplier filings, bank deposit patterns, and third-party payment processor data, and have a fairly specific theory about where the discrepancy lives[2]. Understanding that the process starts as a data-matching exercise, not a human decision to single out a business, changes how it should be handled from the first letter onward.

Key Takeaway

The single most common trigger for a GST/HST audit is not fraud or aggressive claiming, it is an unreconciled mismatch between what a business reports on its GST/HST return and what it reports on its income tax return. Reconciling the two before filing eliminates the single largest source of automated audit flags.

Why Your File Gets Flagged

CRA's compliance program uses risk-based selection rather than pure randomness, drawing on business intelligence and analytics authorized under section 275 of the Excise Tax Act to identify non-compliance patterns, including in sectors like the platform and sharing economy that have historically been under-reported[3]. In practice, the recurring risk indicators are well documented[4][5]:

  • Revenue mismatches between a T2 corporate return and the corresponding GST/HST filings for the same period.
  • Input tax credit claims that are large relative to reported sales, or that spike suddenly compared to prior periods.
  • Cash-intensive industries, restaurants, salons, and construction contractors receive disproportionate scrutiny because cash revenue is structurally easier to under-report before it ever reaches the books.
  • Repeated losses claimed year after year, which can prompt CRA to question whether a business is a genuine commercial activity at all.
  • Prior audit adjustments, a file that was reassessed once is statistically more likely to be selected again.
  • Third-party tips submitted through CRA's Informant Leads Program.

Section 288 of the Excise Tax Act gives CRA auditors broad, but not unlimited, powers: the authority to inspect records, enter business premises at reasonable times, conduct interviews, and require reasonable assistance in verifying GST/HST compliance[6]. Those powers extend further than most business owners expect. Because the Act permits inspection of documents relevant to the obligations of "that or any other person," auditors will sometimes use incomplete corporate records as grounds to request personal bank statements or shareholder documentation, particularly where unreported taxable supplies or commingled funds are suspected[6]. Blanket personal document demands at the outset of a routine audit are not automatically justified, and a structured response, producing corporate records first and requiring the CRA to articulate a specific concern before expanding scope, is a legitimate and commonly used posture[6].

Desk Audit vs. Field Audit

Most GST/HST audits fall into one of two formats, and knowing which one you are in shapes how much disruption to expect[4]:

Desk Audit

Conducted Remotely

The CRA requests documents electronically or by mail. This is the more common format for routine mismatches and smaller businesses, and it can often be resolved entirely through correspondence.

Field Audit

Conducted On-Site

Auditors visit the business premises to examine records and operations directly. Typically reserved for larger businesses, multi-year discrepancies, or cases where the CRA suspects the electronic records do not tell the full story.

The Audit Timeline: What Actually Happens, In Order

Step 1

Notice of Audit

A letter outlining the periods under review and an initial document list. Responding promptly, rather than ignoring it, materially affects how the rest of the process unfolds.

Step 2

Document Request

GST/HST returns, sales invoices, purchase receipts, ITC support, bank statements and general ledgers for the audit period.

Step 3

Proposal Letter

The auditor sets out proposed adjustments before finalizing anything, giving you a defined window to respond with facts and documentation.

Step 4

Notice of (Re)Assessment

The formal result. This document starts the 90-day objection clock, whether or not you agree with it.

You cannot negotiate the underlying tax law during this process, but you can absolutely negotiate the facts and the documentation supporting your position[2]. Auditors are required to give you a genuine opportunity to respond to a proposal before it becomes a final reassessment, and a well-documented response at that stage is far cheaper than fighting the same issue later at Tax Court.

How Input Tax Credit Claims Actually Get Verified

The Excise Tax Act requires registrants to hold "sufficient evidence" before claiming an input tax credit, and the Input Tax Credit Information Regulations set out exactly what that evidence must contain, scaling with the size of the purchase[7]. For purchases under $30, a supplier's name, the invoice date, and the total amount are sufficient. Larger purchases require progressively more detail, including the supplier's GST/HST registration number. CRA's automated systems now cross-reference every claimed supplier number against the official registry in real time, and an invoice bearing an invalid, expired, or mismatched registration number is grounds to deny the credit entirely, even where the underlying purchase was completely legitimate[7].

The Expensive Part of a Denied ITC

A denied input tax credit is not just a repayment of the credit itself. The business absorbs the full GST/HST it already paid to its supplier, effectively paying the tax twice, plus daily-compounding interest calculated from the original claim date, which can add thousands of dollars on a single denied claim discovered years later[7].

The Six-Year Document Rule

Canadian tax law requires adequate books and records to be retained for a minimum of six years from the end of the last tax year to which they relate[5]. In an audit context, that typically means sales records, expense receipts, complete bank statements for every account touching the business, payroll records including T4s and contractor T4A/T5018 slips, detailed GST/HST support for every ITC claimed, and a contemporaneous vehicle logbook for any claimed automobile expenses[5]. Businesses using computerized accounting systems should also expect CRA's Computer Assisted Audit Techniques team to analyze electronic records directly where transaction volume makes manual sampling impractical[9].

Interest Accrual on a $50,000 Denied ITC Claim, Discovered in Year 3

Cumulative Interest at 7% Compounded Annually (Illustrative)

Interest, Penalties, and What a Denial Actually Costs

The CRA's prescribed interest rate is reviewed and updated every calendar quarter, calculated as the federal short-term rate plus four percentage points, and stood at 7% annually, compounded daily, for the quarter running July 1 through September 30, 2026[8]. Late-filing penalties on a GST/HST return with a balance owing follow a separate formula: 1% of the balance owing, plus 0.25% for every full month the return remains outstanding, to a maximum of twelve months[8]. Interest is charged in addition to any penalty, not instead of it, and this interest is not deductible for income tax purposes, making it a pure, unrecoverable cost to the business[7].

Your Appeal Rights: The 90-Day Clock

If you disagree with a reassessment, the Excise Tax Act gives you exactly 90 days from the date the Notice of Assessment or Reassessment was sent, not the date you opened it, to file a formal Notice of Objection on Form T400A[10]. Unlike personal income tax objections, which carry an extended one-year deadline for individuals, GST/HST objections carry no such extension: the 90-day window applies uniformly to every registrant, corporate or individual[10]. Missing it extinguishes your right to object entirely, though a narrow extension process exists if you can show you intended to object within the deadline and were prevented by circumstances beyond your control[10].

An independent Appeals Officer, someone who was not involved in the original audit, reviews the objection and can confirm the assessment, vary it, or vacate it entirely, typically within about 180 days[11]. If the outcome still is not acceptable, the next step is the Tax Court of Canada, which must also be petitioned within 90 days of the Appeals decision. Disputes involving $50,000 or less in GST/HST can proceed under the Tax Court's informal procedure, with no filing fee, no lawyer strictly required, and a hearing typically scheduled within about 12 months[12]. Larger or more complex disputes proceed under the general procedure, a substantially longer and more expensive process where legal representation is strongly advisable.

A Practical Note on Paying During a Dispute

Filing an objection does not pause CRA's collection activity for GST/HST, unlike for personal and corporate income tax. Interest continues to accrue on the disputed balance throughout the objection process regardless. Many advisors recommend paying the disputed amount under protest while the objection proceeds, since a successful objection results in a full refund with interest, while an unpaid balance simply keeps accruing cost if the objection fails[11].

The Verification Protocol: A Practical Defence Framework

  1. Reconcile GST/HST filings against your T2 before filing either. This single step eliminates the most common automated audit trigger.
  2. Validate every supplier's GST/HST number at the time of purchase, not years later during an audit, when the supplier may no longer be reachable.
  3. Retain six full years of records, organized by reporting period, not just by calendar year.
  4. Respond to every CRA letter within its stated deadline, even if the response is simply a request for more time.
  5. Sequence document production carefully if the request expands beyond routine GST/HST support into personal financial records.
  6. Treat the proposal letter as your real opportunity to argue the facts, not the final reassessment.
  7. Calendar the 90-day objection deadline the day the notice arrives, not the day you decide to act on it.

Frequently Asked Questions

How far back can the CRA audit my GST/HST filings?
The normal reassessment period is generally four years for most GST/HST registrants, but there is no time limit at all where the CRA establishes misrepresentation attributable to neglect, carelessness, or fraud, which is precisely why six years of clean records is the safer practical standard.
Does filing a Notice of Objection stop the CRA from collecting?
For GST/HST and payroll source deductions, no. The CRA can continue collection activity even while your objection is under review, which is different from the income tax rules. This is one of the more commonly misunderstood points in the entire dispute process.
What if I find an error in my own GST/HST filing before the CRA does?
Correcting it proactively through CRA My Business Account's "Adjust a return" tool, or through the Voluntary Disclosures Program for more serious omissions, is treated very differently than the same error being discovered during an audit. Voluntary, complete disclosures made before CRA contact can materially reduce or eliminate penalties.
Is a field audit worse than a desk audit?
Not inherently, but it usually signals a more complex or higher-dollar file. A field audit involves more disruption to daily operations, and it is worth having a bookkeeper or accountant present, or at minimum reachable, throughout.
IB

About The Insight Bureau Research Desk

The Insight Bureau is GSH Financial's research publication, written by our audit protection practice for Canadian business owners. This article reflects CRA administrative guidance and current published interest rates as of publication; see References below.

References

  1. Insight Accounting CPA. (2026, May 20). CRA audit help 2026: What to do if the CRA audits your small business in Canada. insightscpa.ca/.../cra-audit-help-2026
  2. Easy Cost Living. (2026, January 15). GST HST audit Canada 2026: What to expect, CRA examination. easycostliving.ca/gst-hst-audit-what-to-expect
  3. Canada Revenue Agency. (2024, November 8). GST/HST audit and examination [Privacy impact assessment]. Government of Canada. canada.ca/.../gst-hst-audit-examination.html
  4. KWB LLP Accountants. (2026). CRA audit activity: Prepare your business for 2026. kwbllp.com/blog/cra-audit-activity-2026
  5. Insight Accounting CPA. (2026, May 20). CRA audit help 2026, record-keeping requirements section. insightscpa.ca/.../cra-audit-help-2026
  6. Kirshen Tax Law. (2026, February 25). CRA corporate GST/HST audit powers. kirshentaxlaw.ca/cra-corporate-gst-hst-audit-powers-canada
  7. Signzy. (2026, January 16). Canada GST verification: Free and paid methods. signzy.com/blogs/canada-gst-verification-using-official-registry-automation
  8. RGB Accounting. (2026, June 30). CRA interest rates remain at 7%: Why late tax payments can cost more than you think in 2026. rgbaccounting.com/.../cra-interest-rates-remain-at-7
  9. Canada Revenue Agency. (2026, March). Income tax audit manual [Domestic Compliance Programs Branch]. Government of Canada. canada.ca/.../income-tax-audit-manual
  10. Taxpayer.law. (2026, January 19). T400A Notice of Objection: Income Tax Act and Excise Tax Act (GST/HST) guide. taxpayer.law/t400a-notice-of-objection
  11. Canadian Money Help. (2026, May 4). CRA notice of reassessment: What it means and how to respond. canadianmoneyhelp.ca/articles/cra-notice-of-reassessment-canada
  12. CATaxTools. (2026, June 27). CRA notice of reassessment 2026: 90-day objection window and how to push back. catax.tools/tax-insights/cra-notice-of-reassessment-objection-2026

This article reflects CRA administrative guidance and prescribed interest rates current as of publication and is provided for general informational purposes. It is not tax or legal advice for any specific business. Interest rates change quarterly, confirm the current rate at canada.ca before making any payment or filing decision.