How to Correct a GST/QST Return After Filing (Amendment Process) — Montreal CPA Firm

Mistakes happen. Whether it’s missing an invoice, entering the wrong tax amount, misclassifying a transaction, or forgetting to claim ITCs/ITRs, errors in GST/QST returns are extremely common. But correcting a return incorrectly can trigger reviews, refund delays, or full audits. This guide explains how to safely amend a GST or QST return using Mackisen’s precise correction process.

Why Correcting GST/QST Matters
A wrong number can cause repayments, denied refunds, or assessments. Correcting mistakes quickly and properly protects your compliance record and cash flow.

Legal and Regulatory Framework
GST amendments fall under the Excise Tax Act through CRA’s adjustment system. QST amendments fall under the Tax Administration Act through Revenue Québec’s FPZ-500-V adjustments. Hickman Motors (1997) reinforces proof requirements. Lac d’Amiante (2001) confirms that corrections must be documented fully.

What Happens If You Don’t Correct Mistakes
Imagine discovering an error months later: you overstated GST collected by $12,000. Because you never corrected the return, CRA believes you owe the amount. Meanwhile, your next refund is frozen until the discrepancy is resolved. Your business faces cash flow distress and potential audit expansion. Avoiding or ignoring mistakes only worsens the situation.

Learning Section: When You Must File an Amendment
You must amend when:
You reported wrong revenue
You claimed incorrect ITCs/ITRs
You missed filing a credit note
You forgot to report GST/QST collected
Your accounting system miscalculated tax
The filing period contained incorrect adjustments

SEO Learning: Primary and Secondary Keywords
Primary: amend GST return, correct QST return Quebec, GST QST adjustment guide.
Secondary: Revenue Québec FPZ-500-V correction, CRA GST adjustment, Montreal CPA tax corrections.

How to Correct a GST Return
Log into CRA My Business Account
Select “Adjust a return”
Choose the filing period
Enter corrected numbers
Upload documents if requested
Save confirmation

How to Correct a QST Return
Log into Mon Dossier
Select FPZ-500-V adjustments
Enter corrected values
Submit supporting documents
Save confirmation receipt

Documentation Section
Original return
Corrected return
Invoices
Proof of payment
Reconciliation calculations
Internal error explanation
All must be kept for six years.

Common Mistakes
Adjusting without documentation
Submitting incorrect adjustment periods
Claiming ITCs/ITRs without proof
Failing to reconcile before amending
Ignoring CRA/RQ follow-up messages

Winning With Revenue Québec and Canada
Mackisen prepares a fully documented amendment package, reconciles your accounts, responds to CRA/RQ inquiries, and ensures your correction does not trigger unwanted audits.

Mackisen Service Hub
We manage all GST/QST amendments, prepare documentation, communicate with tax authorities, and ensure accurate corrections.

Why Mackisen
With 35+ years of CPA experience, Mackisen ensures GST/QST amendments are accurate, defensible, and stress-free.