Correcting a Mistake on a Filed HST Return in Ontario

Finding an error on an HST return you already submitted is uncomfortable, but it's also common — a missed input tax credit, a revenue figure entered wrong, a supply that was classified incorrectly. What you do next depends heavily on what kind of error it is, whether CRA has already caught it, and how large the amount involved is.

This guide walks through the decision points in order: how to tell what kind of correction you're dealing with, how to fix a simple error yourself, and when the situation calls for a more formal process instead.

Why Corrections Happen

Most HST return errors fall into a few common categories: a math or data-entry mistake, a missed or incorrectly claimed input tax credit, a supply that was zero-rated or exempt but taxed (or vice versa), or a more substantial issue like unreported revenue across multiple periods. The size and nature of the error is what determines the right path forward — a small clerical fix is handled very differently from a pattern of unreported income.

Step 1: Figure Out What Kind of Error You're Dealing With

Before doing anything else, get clear on:

• How much money is involved, in either direction.
• Whether the error affects one period or several.
• Whether it was a genuine mistake or reflects a more systemic gap in how the business has been reporting.
• Whether CRA has already contacted you about this return or this issue in any way.

The answers to these questions determine whether a simple adjustment request is enough or whether you need a more formal process.

Step 2: Amending a Return You Haven't Been Contacted About

For most straightforward errors that CRA hasn't already flagged, you can request an adjustment to the previously filed return — correcting the reported amounts through your CRA business account or the applicable request process, rather than trying to "re-file" the whole return from scratch. Keep clear documentation showing what the original entry was, what the corrected figure should be, and why the change is accurate, since CRA can ask you to substantiate any adjustment.

Step 3: If CRA Has Already Reassessed You — Objecting Instead

If CRA has already audited or reassessed the return and you disagree with the result, the correction path changes: you file a formal Notice of Objection with the CRA Appeals Branch rather than a simple adjustment request. An objection is an administrative step, separate from and prior to any court proceeding — you cannot go straight to the Tax Court of Canada without objecting first (or without CRA failing to respond to your objection within the statutory waiting period). The deadline to object is shown on your notice of reassessment; confirm it there rather than assuming a generic timeframe, since it depends on the type of taxpayer and the type of assessment involved.

Step 4: If the Error Involves Unreported Amounts, Consider the Voluntary Disclosures Program

If the correction involves previously unreported revenue, overclaimed input tax credits, or another issue that carries real penalty or interest exposure, a straightforward adjustment request may not be the right tool — the Voluntary Disclosures Program (VDP) might be. Under the CRA's current VDP framework (in effect since October 1, 2025), applications fall into two categories:

• Unprompted applications — made before CRA has contacted you about the specific issue — generally receive the most favourable relief on penalties and a meaningful reduction in interest.
• Prompted applications — made after some CRA contact about the issue, such as an education letter, but before enforcement action like an audit — can still qualify for relief, though generally at a reduced level compared to unprompted applications.

The VDP never relieves the underlying tax you owe — it only addresses penalties and, in part, interest — and every application is reviewed and decided by CRA on its own facts; relief is discretionary, not automatic. As of mid-2026 the relief percentages associated with each category were meaningful but specific — verify the current figures with a tax professional before relying on a number you've seen elsewhere, since program details can be updated.

Keeping Records That Support Your Correction

Whichever path applies, document your correction thoroughly:

• [ ] The original figure as filed and the corrected figure, side by side.
• [ ] The source documents supporting the correction (invoices, contracts, bank records).
• [ ] A written explanation of how the error occurred.
• [ ] Copies of any correspondence with CRA about the issue, dated.
• [ ] A note of which process you used — adjustment request, objection, or VDP application — and when you submitted it.

Frequently asked questions