WHAT IF I MADE A MISTAKE ON A GST/QST RETURN?

Every Quebec business eventually makes an error on a GST/QST return — and that’s normal. Maybe a receipt was missing, a sales invoice was entered late, a tax code was wrong, or a POS miscalculated the taxes. The important thing is knowing how to correct the mistake quickly and properly. This guide explains what happens when you make an error on a GST/QST return, how to fix it, and how to avoid penalties or delays with Revenue Québec.

Timely correction protects your business from reassessments, interest charges, and future audit complications.

LEGAL AND REGULATORY FRAMEWORK

Corrections to GST/QST returns fall under:

• the Excise Tax Act (GST)
• the Quebec Taxation Act (QST)

Businesses are legally required to:

• file accurate returns
• correct mistakes when discovered
• maintain documentation that supports the revised amounts

Revenue Québec allows businesses to correct past returns through:

• adjustments
• amended returns
• self-assessment entries
• voluntary correction filings

KEY COURT DECISIONS

Courts have ruled that:

• taxpayers must correct errors as soon as they are aware of them
• “I didn’t know” or “my employee made a mistake” is not a defense
• input tax credits without proper documentation must be denied
• Revenue Québec may reassess incorrect filings even years later
• voluntary corrections can reduce penalties, but do not eliminate interest

The jurisprudence emphasizes accuracy and timely correction.

WHY GST/QST ERRORS HAPPEN

Common causes include:

• incorrect tax coding in accounting software
• POS system misconfiguration
• missing or illegible invoices
• claiming ITCs/ITRs without supporting documents
• reporting sales in the wrong period
• double-counting expenses
• forgetting to include credit notes
• incorrect interprovincial tax treatment
• misunderstanding zero-rated vs. exempt rules
• late bookkeeping

Errors happen — the key is how quickly they are fixed.

WHAT IF YOU MADE A MISTAKE ON A GST/QST RETURN? HERE’S WHAT TO DO:

1. Identify the mistake clearly

Review your accounting records, POS reports, invoices, and supplier receipts to identify:

• what period is affected
• whether it impacts GST, QST, or both
• whether it increases or decreases tax payable
• whether it relates to sales, purchases, or adjustments

2. Determine if you need an adjustment or an amended return

Adjustments

Use adjustments when the mistake is small and affects a single line item (ex: a missing receipt, incorrect ITC amount).

Amended return

Use an amended return when the mistake significantly affects:

• taxable sales
• total GST/QST collected
• large or multiple ITCs/ITRs
• incorrect filing period
• major misstatements

If unsure, a CPA can decide the correct method.

3. Prepare supporting documentation

Revenue Québec may request proof, such as:

• the original incorrect invoice
• the corrected invoice
• updated expense documentation
• bank statements
• reconciliation schedules
• credit notes
• corrected POS reports

Documentation is essential during verification.

4. Make the correction through Revenue Québec

Corrections can be submitted via:

• Mon Dossier online portal (preferred)
• filing a paper request for adjustments
• submitting an amended FPZ-500-V return
• voluntary disclosure (for serious or long-term errors)

5. Pay any additional tax owing

If the correction increases tax payable, pay it immediately to minimize interest.

6. Monitor for refund or verification

If the correction increases your refund:

• Revenue Québec may request documentation
• Refunds may be held until verification is complete

This is normal and not a cause for concern if records are clean.

7. Correct your accounting system to prevent recurrence

Errors often come from:

• wrong GST/QST tax codes
• duplicated transactions
• missing receipts
• POS misconfiguration
• manual overrides

Fixing the root cause prevents repeat mistakes.

TYPES OF GST/QST MISTAKES AND HOW TO FIX THEM

Underreported sales

Submit an adjustment or amended return and remit the additional tax.

Overreported sales

Submit an adjustment and claim the correction in the next return.

Incorrect ITCs/ITRs

Provide documentation and adjust the specific period.

Missing invoices

Request duplicates from suppliers and correct the return.

Wrong tax coding (ex: charged GST only instead of GST+QST)

Amend the return and correct invoicing practices.

Incorrect place-of-supply (charged QST to Ontario customer)

Issue corrected invoices and amend filings.

Filing for the wrong period

Submit an amended return for the correct period.

WHEN SHOULD YOU CALL A CPA?

You should seek help when:

• the correction affects multiple periods
• mistakes involve interprovincial rules
• the correction is substantial
• a refund is being held for verification
• Revenue Québec has issued a notice of assessment
• you are unsure how to document corrections
• your accounting system is inconsistent

MACKISEN STRATEGY

Mackisen CPA specializes in GST/QST corrections. We:

• identify incorrect filings
• correct errors through adjustments or amended returns
• rebuild proper supporting documentation
• reconcile GST/QST accounts
• respond to verification letters
• prevent recurring system issues

Our structured correction process reduces interest, protects against penalties, and ensures smooth compliance with Revenue Québec.

REAL CLIENT EXPERIENCE

A Montreal retailer underreported QST due to a POS malfunction. Mackisen amended returns and negotiated interest relief.

A consultant claimed ITCs without receipts. Mackisen reconstructed documentation and corrected filings.

An e-commerce seller misapplied interprovincial tax. Mackisen filed adjustments and avoided reassessment.

COMMON QUESTIONS

Can I fix a GST/QST return myself?
Yes but errors can worsen the problem. A CPA is recommended for major corrections.

Will Revenue Québec penalize me for correcting a mistake?
Penalties may apply, but voluntary corrections often reduce consequences.

Is there a deadline to amend a return?
Yes. Adjustments must be made within statutory time limits (varies by tax).

Does correcting a return trigger an audit?
Not necessarily but poor documentation increases the risk.

WHY MACKISEN

With more than 35 years of combined CPA experience, Mackisen CPA Montreal helps businesses correct GST/QST mistakes efficiently and accurately. We minimize financial impact and ensure your records are fully compliant.