You have to register for GST/HST when you no longer qualify as a small supplier because your total worldwide taxable supplies of goods and services exceed the small supplier limit of $30,000 in a year
You have to register for GST/HST if you are a taxi or limousine operator whose fares are regulated by federal or provincial laws, even if your revenues do not exceed $30,000.*
These are requirements for all type of business: self-employed, sole proprietor, partnership, and corporation.
One thing you have to know is that you will have to calculate HST for the entire year, not only after the $30,000 sales. For example if you reach the value of sale of $ 30,000 within the period January-April, you will pay HST for the entire year. The CRA is calculating taxes on the first 30,000 even though you did not charge your customers.
Advice: If you project that your annual sales/services will be at least $30,000 you should register for HST and charge your customers accordingly.
For more about this topic you can contact me by e-mail at firstname.lastname@example.org.
Nicole Dronca, Accountant and Tax Preparer
* Canada Revenue Agency website, http://www.cra-arc.gc.ca/tx/bsnss/tpcs/gst-tps/rgstrng/mndtry-eng.html