If your worldwide taxable revenue crosses $30,000 and you keep operating without registering for GST/HST, the CRA can register your business retroactively to the date you should have registered, assess the GST/HST you should have collected on every taxable sale since then, and add penalty and interest on top. You generally cannot go back and bill past customers for tax you didn't charge at the time — so the assessed amount usually comes out of money you've already spent, not out of a fresh invoice. This page covers the trigger, the retroactive exposure, and the practical cost of staying unregistered past the threshold. For how to register correctly the first time, see our GST/HST registration guide.
The trigger: the $30,000 small-supplier threshold
Registration stops being optional the moment your business crosses $30,000 in worldwide taxable revenue — either in a single calendar quarter or cumulatively across four consecutive quarters. Below that line you're a small supplier and registration is a choice (see our voluntary registration guide for when that choice pays off). Above it, registration is mandatory, and the clock starts on the sale that crossed the line: you have 29 days from that sale to register. Nothing about crossing the threshold quietly resets it — the obligation exists whether or not you noticed.
What the CRA can assess retroactively
This is the core exposure, and it has three parts:
- The uncollected tax itself. The CRA can assess GST/HST on your taxable sales going back to the date you were required to register — not the date you actually register. If you crossed $30,000 eighteen months ago and are still unregistered, the exposure covers that whole period.
- Penalty and interest. Late registration is a compliance failure like any other missed filing, and it draws both a penalty and arrears interest on the amount owing. The exact mechanics are set by the CRA and can change; confirm the current figures directly with the CRA or a qualified accountant rather than assuming a prior year's rate still applies — the durable point is that both a penalty and interest apply, not a specific percentage.
- No offsetting relief for the customer-facing side. Because the tax was never charged on the original sale, there's no natural way to recover it from the customer after the fact. Some businesses can go back and invoice for it; many can't, either because the relationship has ended or because retroactively taxing a past sale simply isn't commercially realistic.
Why the exposure keeps growing the longer you wait
The retroactive assessment isn't capped to the current or prior calendar year the way an ordinary tax return correction can be, because no GST/HST return was ever filed for the unregistered period — there's no filed return starting a normal reassessment clock. In practice this means the cost of staying unregistered doesn't level off; it accumulates with every additional taxable sale you make while over the threshold and unregistered.
The practical exposure, put simply
- You lose the ability to price the tax into your sales. A registered business bills GST/HST on top of its price; an unregistered business found to have owed it must usually absorb the amount out of revenue already booked.
- You lose input tax credits for the same period. Registration retroactively doesn't just create a tax bill — it also opens the door to claiming input tax credits on your business purchases for that period, which at least partially offsets the exposure. Missing this step means paying the full assessed amount with none of the available offset.
- The gap compounds with scale. A business that crossed $30,000 modestly and stayed unregistered for a few months faces a very different number than one that grew well past the threshold and stayed unregistered for years.
The same exposure applies to a non-resident business selling into Canada that should have registered and didn't — see our non-resident GST/HST registration guide for which registration path applies before that risk arises.
What to do if you think you're already past the threshold
Register now through Business Registration Online (BRO) — see our step-by-step registration guide for the mechanics — and get professional advice before filing anything retroactively. Voluntarily correcting the position, with a properly modelled retroactive filing and ITC claim, is a materially better outcome than being found unregistered on a CRA review. Model the tax itself with our sales tax calculator, and browse related questions in our GST FAQ hub.
How RN Canada helps
RN Canada is an accounting and advisory firm with offices in Edmonton and Vancouver, led by Ozgur Duymaz, Ph.D., CPA (Canada), ACCA (UK), CMA (US). We assess whether a business has actually crossed the $30,000 threshold, register it correctly with the right effective date, and — where registration is already overdue — model the retroactive exposure and the offsetting input tax credits before approaching the CRA. See our tax return preparation service to get an overdue GST/HST position corrected properly.
Frequently asked questions
The CRA can register your business retroactively to the date you should have registered, then assess the GST/HST you should have collected on your taxable sales since that date — plus penalty and interest. You generally can't go back and bill past customers for tax you didn't charge at the time, so the assessed amount often comes straight out of revenue you already spent.
No meaningful one. Once your worldwide taxable revenue passes $30,000 in a single calendar quarter or over four consecutive quarters, registration is mandatory from the date of the sale that crossed the threshold, and you have 29 days to register. Missing that window doesn't delay when your obligation started — it just delays when the CRA finds out.
Yes. An assessment for a period where you should have been registered isn't bounded by the normal reassessment-period rules that protect a filed, assessed return, because no return was ever filed for that period. The longer a business operates above the threshold without registering, the larger the retroactive exposure grows.
Generally yes. The obligation to remit tax on a taxable sale doesn't depend on whether you charged your customer for it. If you should have collected GST/HST and didn't, the CRA can still assess you for the amount, which means the shortfall is effectively absorbed by the business rather than the customer.
Yes, if the $30,000 test is genuinely not met. The risk is specifically for businesses that crossed the small-supplier threshold — in a single quarter or across four consecutive quarters — and kept operating unregistered, whether by oversight or by miscounting revenue against the rolling test.
Register now and get professional advice before you file anything retroactively. Voluntarily coming forward and correcting the position is a materially better posture with the CRA than being found unregistered on review, and an accountant can model the actual exposure before you approach the CRA.