Do I have to register for GST/HST yet?

Behind the numbers.

You are a small supplier , and so not required to register: while your worldwide taxable supplies stay at or below $30,000. The number counts revenue from associated businesses too, and excludes exempt supplies and sales of capital property.

Two tests can end that status, and the difference between them is a month of runway:

• One calendar quarter. If a single quarter alone goes over $30,000, small-supplier status ends immediately. Registration is effective the day of the supply that crossed the line, and that supply is itself taxable: you charge on the invoice that took you over.
• Four consecutive quarters. If the running total over four quarters goes over $30,000 but no single quarter did, status ends at the end of the month following that quarter. Supplies you make in that intervening month are generally still untaxed.

That second rule is the one most often missed, and it explains a result that otherwise looks wrong: a business can cross $30,000 in March and still be correctly not charging tax through April.

Registering voluntarily before you have to is often worth it: a registrant can claim input tax credits on what they buy, which a small supplier cannot.