Most people know there is a $30,000 threshold for GST registration. Fewer know how it is measured, and that is where the trouble starts.
In Alberta there is no provincial sales tax, so GST is the only sales tax to think about — simpler than most of the country, and easy to stop watching for exactly that reason.
It is a rolling four-quarter test
You stop being a small supplier when your worldwide taxable revenue exceeds $30,000 over four consecutive calendar quarters — not over a fiscal year, and not over a calendar year. The test runs continuously.
There is also a single-quarter rule: exceed $30,000 in one quarter alone and you cease to be a small supplier immediately, effective on the sale that pushed you over.
The two rules have different clocks
This is the part worth getting right, because the two tests do not bite at the same moment.
Cross the threshold gradually, over four consecutive quarters, and you stop being a small supplier at the end of the month following the quarter in which you crossed. Your effective registration date is the day of your first sale after that, and you have 29 days from that date to register. So there is a short grace period built in.
Cross it inside a single quarter and there is no grace period at all. You cease to be a small supplier on the sale that took you over, that sale is itself taxable, and you have 29 days from it to register.
Why that matters
From your effective date you are required to charge GST, whether or not you have noticed. If it takes you four months to work that out, you have four months of sales on which tax should have been collected and was not.
CRA will still expect the tax. You can either go back to clients and ask for more money on invoices they have already paid, or absorb it out of your own margin.
Selling outside Alberta changes the rate
This is the part that catches Alberta businesses selling into other provinces. The rate is generally determined by where the customer is, not where you are. Sell to a client in Ontario and the place-of-supply rules will usually have you charging HST at Ontario's rate, not Alberta's 5%.
Businesses that have only ever charged 5% often discover this after they have been invoicing out of province for a year.
The part that softens it
Registration also lets you claim input tax credits on the GST you pay on business purchases. For a business with meaningful expenses — equipment, fuel, subcontractors, professional fees — registering is often not the burden it looks like.
For businesses selling mainly to other registered businesses, voluntary early registration frequently makes sense. Your clients claim the tax back, so your price is effectively unchanged to them, and you start recovering tax on your own costs immediately.
Practical advice
Track the rolling four-quarter figure, not the annual one. If you are within a few thousand dollars of the threshold, register before you cross rather than after — the grace period is measured in weeks, and it is not the kind of thing you want to be reconstructing later. And if you have started selling outside Alberta, check the place-of-supply rules before the next invoice goes out, not after twelve of them have.
General information only, current at the date of publication. Tax rules and CRA positions change. This is not advice for your circumstances.