- Once your revenue from taxable supplies crosses the threshold set out in the Excise Tax Act, registration is mandatory, not optional — and it's based on rolling revenue, not your prior…
- - [ ] Charging the wrong rate, or no tax, on out-of-province sales.
- - [ ] Not keeping proper supporting documentation.
Most new Ontario business owners learn HST compliance the same way — by making a mistake, catching it late, or getting a letter from the CRA about it. The rules themselves aren't especially complicated, but the details are easy to get wrong when you're focused on actually running the business.
This checklist rounds up the errors that come up again and again in the first year or two of a new Ontario business's HST life, grouped by where they typically happen.
Registration Mistakes
- [ ] Waiting too long to register. Once your revenue from taxable supplies crosses the threshold set out in the Excise Tax Act, registration is mandatory, not optional — and it's based on rolling revenue, not your prior year's tax return. Confirm the current threshold rather than relying on a number you've seen elsewhere.
- [ ] Registering under the wrong entity. A sole proprietor who later incorporates needs to register the new corporation separately — an HST number doesn't automatically transfer just because the business "is basically the same."
- [ ] Not considering voluntary registration. Businesses below the mandatory threshold can often register anyway to start claiming input tax credits. Skipping this without weighing it can mean leaving recoverable tax on the table.
Collection and Rate Mistakes
- [ ] Charging the wrong rate, or no tax, on out-of-province sales. HST and GST rates vary by province, and where the tax applies depends on rules about where the supply is made — not simply where your business is located.
- [ ] Treating exempt and zero-rated supplies the same. Both mean no tax is charged, but only zero-rated supplies let you claim input tax credits on related costs. Mixing them up distorts your net tax calculation.
- [ ] Forgetting HST applies to non-cash transactions. Bartered services, trade-ins, and goods exchanged for other goods are still taxable supplies valued at fair market value — no cash changing hands doesn't mean no tax applies.
- [ ] Assuming the current Ontario HST rate without checking. Ontario's HST rate combines a federal and a provincial component — it has been 13% for years, but confirm the current rate before applying it, since rate changes (however rare) apply from a specific effective date.
Input Tax Credit Mistakes
- [ ] Not keeping proper supporting documentation. An ITC claim needs to be backed by invoices and receipts that meet CRA's documentation requirements — a credit card statement alone usually isn't enough.
- [ ] Claiming ITCs on personal or mixed-use expenses without apportioning. Only the business-use portion of a mixed expense is eligible, and CRA reviews this closely.
- [ ] Missing ITCs entirely on a return because the bookkeeping wasn't set up to track HST paid separately from the underlying expense.
Filing and Remittance Mistakes
- [ ] Getting the filing frequency wrong. New registrants are assigned a reporting period based on revenue, and it can change as the business grows — filing on the wrong schedule creates avoidable late-filing issues.
- [ ] Confusing collecting HST with remitting it. The HST a business collects from customers isn't the business's money — it's held for the CRA, and spending it as working capital instead of remitting it is one of the more serious mistakes a cash-strapped new business can make.
- [ ] Missing the closely related corporations election in a multi-entity structure, and charging HST unnecessarily on intercompany transactions that could have been simplified.
- [ ] Filing nil returns late, or not at all, on the assumption that no activity means no filing obligation — a registered business generally still has to file for every reporting period, even a quiet one.
Why These Mistakes Compound
Individually, most of these errors look small — a missed receipt here, a late filing there. The problem is that HST errors tend to compound across every reporting period until someone notices, whether that's your bookkeeper, an accountant doing year-end cleanup, or a CRA reviewer. A wrong rate applied consistently for a year is a much bigger fix than the same mistake caught after one invoice.
Frequently asked questions
I just registered — do I need to go back and fix past invoices?
If the invoices predate your registration and you weren't yet required to register, generally no. If you registered late and should have been charging HST earlier, that's a different and more serious situation — see our article on the penalty for late HST registration.
Can my bookkeeper handle all of this, or do I need a lawyer?
Day-to-day HST compliance — collecting, filing, and remitting correctly — is typically bookkeeping and accounting work. A lawyer becomes relevant once the CRA disputes how you've handled something, or when you're structuring a multi-entity business and want the tax consequences reviewed before you commit to a structure.
What's the fastest way to tell if I'm making one of these mistakes?
A short review of your last several HST returns against your actual invoices and receipts usually surfaces the obvious gaps — mismatched rates, missing ITC documentation, or a filing frequency that doesn't match your current revenue.
Does the CRA go easier on new businesses that make honest mistakes?
There's no blanket leniency for being new, but genuine errors caught and corrected before the CRA finds them are treated very differently than the same errors discovered on audit. Fixing a mistake proactively is almost always the better position to be in.
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