For Canadians:

If you have chosen to start your business operations as a small supplier, you basically lose your small supplier status and have to register for GST when your revenue (before expenses) exceeds $30,000 (for sole proprietors, partnerships and corporations).

So if your revenue tops $30,000 in one calendar quarter, the Canada Revenue Agency considers you a GST registrant and you:

have to collect GST HST on the supply that made your revenue go over $30,000;
have to register within 29 days of the day that you made the supply that made your revenue go over $30,000.
If your revenue does not top $30,000 in one calendar quarter but does exceed $30,000 over four consecutive calendar quarters, you:

are considered to be a small supplier over that time and for one month after those four quarters;
lose your small supplier status on the day you make the first supply after this period and have to register for the GST within 29 days of this date.


Information from this site: http://sbinfocanada.about.com/od/gst...egisterGST.htm