The Penalty for Not Registering for HST When You Should Have in Ontario

Plenty of Ontario businesses start out below the radar — a side hustle that grows, a freelance practice that picks up steam, a consulting business that quietly crosses into "should have registered months ago" territory. The trouble is that HST registration is not optional once you're required to register, and the CRA does not forgive the gap just because it was an honest oversight.

If the CRA determines you should have registered for HST earlier than you did, the consequences reach backward, not just forward. This article explains what happens once that determination is made, and what your realistic options are if you think you're already behind.

When Registration Stops Being Optional

Every GST/HST registrant crosses a revenue threshold set out in the Excise Tax Act at some point — once your revenue from taxable supplies passes that line, you're required to register, whether or not you got around to it. That threshold is a specific dollar figure that can change, so don't rely on a number you read somewhere; confirm the current figure before assuming you're under it.

The trigger isn't your net income or your profit — it's your gross revenue from taxable supplies, calculated on a rolling basis, not just your prior calendar year. A business that assumes it's "still small" based on last year's tax return can be surprised to learn it crossed the line mid-year.

What Happens Once the CRA Catches Up

If the CRA reviews or audits your business and concludes you should have been registered and charging HST from an earlier date, it can:

1. Deem you to have collected HST from that earlier date — even if you never actually charged your customers. You generally can't go back and bill clients for tax you should have collected months or years ago, which means the amount often comes out of your own pocket.
2. Assess you for that uncollected tax, plus arrears interest calculated from when it should have been remitted. The CRA's prescribed arrears interest rate moves quarterly — it was around 7% as of mid-2026, but verify the current quarterly rate before estimating what you might owe, since it compounds and adds up faster than a flat annual rate suggests.
3. Register you retroactively to the date it determines you should have registered, which then governs every return and remittance from that point forward.
4. Consider a separate penalty for failing to register when required. The CRA does not publish a single flat number for this — how it's calculated depends on the circumstances — so don't assume any figure you've heard is what will actually apply to you.

On the other side of the ledger, you may also be entitled to claim input tax credits for eligible HST paid on your business purchases during that same retroactive period — an assessment that goes back also opens the door to credits you never claimed, which can meaningfully offset what you owe.

Why This Often Gets Worse Before It Gets Better

Retroactive registration isn't a single clean fix — it usually means reconstructing your revenue and expenses for the entire period in question, filing multiple back returns, and reconciling each period's net tax separately. Businesses that discover the problem themselves are almost always better positioned than businesses the CRA catches first, because self-reported gaps can qualify for meaningfully better treatment.

If You Think You're Already Behind: The Voluntary Disclosures Program

The CRA's Voluntary Disclosures Program (VDP) exists for exactly this kind of situation — a filing or registration gap that hasn't yet been caught. As of its most recent overhaul, the VDP distinguishes between two tracks:

• Unprompted applications — made before the CRA has contacted you about the issue — can receive the fuller relief the program offers, generally covering both penalties and a substantial portion of interest.
• Prompted applications — made after some CRA contact, such as an educational letter, but before formal enforcement action like an audit — can still qualify, but for reduced relief.

Either way, the VDP does not erase the underlying tax owing; it only addresses penalties and, to varying degrees, interest. And relief is discretionary — the CRA decides case by case, and an application can be refused or only partly granted. Figures for VDP relief change from time to time, so confirm the current percentages before relying on any specific number.

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