How to Correct a GST/QST Return After Filing (Amendment Process)

Introduction

Mistakes happen — especially when managing multiple tax filings. Whether you entered the wrong sales figures, missed input tax credits, or discovered unreported transactions, you can correct your GST (Goods and Services Tax) and QST (Quebec Sales Tax) returns after filing.

This guide from Mackisen CPA Montreal explains how to amend a GST/QST return, the difference between adjustments and corrections, what documentation you’ll need, and how to avoid future filing errors.

Legal and Regulatory Framework

Corrections to GST and QST returns are governed by:

• Excise Tax Act (R.S.C. 1985, c. E-15) — for federal GST/HST.

• Quebec Sales Tax Act (R.S.Q., c. T-0.1) — for provincial QST.

• Tax Administration Act (RLRQ, c. A-6.002) — for recovery, reassessment, and administrative adjustments.

Once a return is filed, it becomes part of your legal tax record. However, both CRA (Canada Revenue Agency) and Revenu Québec allow businesses to submit corrections or adjustments if new information becomes available or if a genuine mistake occurred.

Learning Insight

Amending a return is not a sign of wrongdoing — it’s a professional compliance step that maintains transparency and accuracy in your tax history.

Step-by-Step: How to Correct a GST/QST Return

Step 1 — Identify the Error

Review your filed return and compare it with your accounting records. Common discrepancies include:

• Underreported or overreported sales.

• Missed or duplicated Input Tax Credits (ITCs) or Input Tax Refunds (ITRs).

• Misclassified transactions (e.g., exempt vs taxable).

• Forgotten adjustments such as discounts, returns, or bad debts.

Document the source and nature of the error — your CPA will need this for the correction request.

Step 2 — Verify the Filing Period

Corrections must be made for the same period in which the error occurred.
For example:

• If you missed $500 in ITCs from March 2025, amend the Q1 2025 return, not your current quarter.

Each tax period stands alone in CRA and Revenu Québec’s systems.

Step 3 — Check If the Error Can Be Adjusted in the Next Return

For small adjustments, you can often include the correction in your next return instead of amending the previous one.

Acceptable cases for adjustment in the next return:

• Small rounding or timing differences.

• Late-arriving invoices for the immediately following period.

When to file an official amendment:

• Errors that significantly affect the tax payable/refundable.

• Errors discovered months or years later.

• CRA/Revenu Québec request a formal correction.

Learning Insight

CRA and Revenu Québec prefer prompt self-correction. Filing amendments before an audit shows good faith and may prevent penalties or reassessments.

Step 4 — Prepare the Supporting Documentation

Keep and organize:

• The original filed return.

• Revised calculations or reports (GST/QST summary, trial balance).

• Corrected invoices, receipts, or journal entries.

• Explanatory note describing the reason for correction.

These documents form the audit trail required if CRA or Revenu Québec requests verification.

Step 5 — File the Amendment

For QST (Revenu Québec)

1. Go to revenuquebec.ca → Mon dossier pour les entreprises.

2. Navigate to Consumption Taxes → File a Correction (Demande de correction d’une déclaration TVQ).

3. Select the filing period and upload or enter the corrected data.

4. Add a short explanation (e.g., “Adjustment to Input Tax Refunds – missed invoice from March 2025”).

5. Submit electronically and save the confirmation number.

If you prefer paper, you can complete Form FP-500-V – Request for Adjustment to a Consumption Tax Return and mail it to Revenu Québec.

For GST (CRA)

1. Log in to canada.ca/my-business-account.

2. Under your GST/HST (RT) account, select “Adjust a return.”

3. Choose the filing period you want to correct.

4. Enter corrected values and the reason for amendment.

5. Review, submit, and save the confirmation number.

You can also submit Form GST189 – General Application for Rebate or Adjustment if your amendment affects refund amounts.

Step 6 — Wait for Review and Confirmation

CRA and Revenu Québec review amended returns manually.
Processing time:

• Online: 2–6 weeks.

• Paper: 6–10 weeks.

You’ll receive a Notice of Reassessment or Amended Summary showing the adjusted balance, refund, or payment due.

Learning Insight

If you owe additional tax, pay it promptly to stop daily interest. If you’re owed a refund, it will appear in your online account once approved.

Common Errors to Avoid

• Filing an amendment for the wrong period.

• Not explaining the reason for correction.

• Forgetting to adjust both GST and QST when the same error affects both.

• Double-claiming ITCs or ITRs in multiple periods.

• Ignoring confirmation receipts or reassessment notices.

Learning Insight

Keep a “Correction Log” in your accounting records. Each amendment should have a reference number, description, and supporting document list.

Real Quebec Business Example

A Montreal marketing agency missed $2,800 in input tax credits from software subscriptions. Mackisen CPA identified the issue, filed a QST and GST correction online, and recovered the refund within five weeks.

Another retailer overreported QST by $3,200 and ignored the mistake. Revenu Québec discovered it during an audit two years later — too late for correction, and the refund was denied.

Lesson: correct errors early — voluntary amendments save both time and money.

Compliance Checklist

Do

• Compare filed returns with accounting records quarterly.

• Keep proof of all changes and correspondence.

• File corrections as soon as errors are discovered.

• Reconcile GST/QST before year-end.

• Consult your CPA before submitting an amendment.

Don’t

• Wait until an audit to disclose errors.

• File duplicate amendments without response from Revenu Québec.

• Forget to amend both taxes when applicable.

• Delete prior-period entries without documentation.

Mackisen Strategy

At Mackisen CPA Montreal, we help businesses correct and amend GST/QST filings accurately by:

1. Reviewing your accounting data and identifying discrepancies.

2. Preparing all supporting schedules and adjustment reports.

3. Submitting amendments electronically through CRA and Revenu Québec portals.

4. Tracking processing and ensuring refunds or reassessments are applied correctly.

Our CPA team ensures your filings remain transparent, accurate, and fully compliant — even when errors occur.

Why Mackisen

With more than 35 years of combined CPA expertise, Mackisen CPA Montreal helps Quebec businesses maintain perfect compliance with CRA and Revenu Québec. From amendments to audits, we ensure your filings reflect professional precision and legal accuracy.