Most new businesses eventually have to deal with GST/HST, but the rules around when and how catch a lot of first-time owners off guard.
When registration is required
Once your revenue passes the small-supplier threshold, GST/HST registration becomes mandatory — and you can also register voluntarily before that point, which is often worthwhile if you're paying GST/HST on business purchases and want to claim it back. The specific threshold and rates are worth confirming with your accountant or the CRA directly, since they're the kind of figures better checked live than quoted from memory.
Filing frequency
Depending on your revenue, you'll file annually, quarterly, or monthly. Smaller businesses usually start on an annual or quarterly cycle; higher-revenue businesses are pushed to more frequent filing. Whatever the cycle, the obligation to collect and remit doesn't wait for the filing deadline — it accrues from the moment you're registered.
Where businesses usually trip up
The most common issues are straightforward: not registering when required (and having to catch up retroactively), forgetting to charge GST/HST on all taxable supplies, or missing input tax credits on legitimate business purchases because the receipts weren't tracked properly. None of these are complicated to avoid — they mostly come down to having bookkeeping that's current enough to catch them before a filing deadline, not after.