If you are a small supplier, GST/HST registration is optional. But you have no choice but to register if you are no longer a small supplier. The effective date of your GST/HST registration depends on when you go over the small supplier threshold amount of $30,000. Here are two typical scenarios:
1). Revenues are over the threshold amount in one calendar quarter
The effective date of registration is the day of the supply that made you go over the threshold amount.
You have 29 days from this day to apply for registration.
Example
The sales of ABC Co. during the first three quarters ending September 30, 2012, were $20,000, meaning it was still a small supplier. In the quarter from October 1 to December 31, it had sales of $35,000. On November 20, an order of $15,000 pushed its taxable sales above $30,000 for the quarter.
That means ABC Co. was no longer a small supplier as of November 20 and it had to charge the GST/HST on the $15,000 sale and any taxable sale made after that.
ABC Co. had 29 days after November 20 to register. Although ABC Co. is considered to be a GST/HST registrant as of November 20, it has until December 19, 2012 to be registered.
2). Revenues are under threshold amount in one calendar quarter, but are over the threshold amount during four consecutive calendar quarters.
You are considered to be a small supplier for those four calendar quarters and a month following those quarters. Your effective date of registration would be the day the first supply was made after you cease being a small supplier.
You have 29 days from this day to apply for the GST/HST.
Example
The sales of ABC Co. during the first three quarters ending September 30, 2012, were $20,000. Its sales in the quarter ended December 31 were $25,000 (less than $30,000 for the quarter but more than $30,000 over four quarters).
ABC Co. is a small supplier until January 31, 2013. Any taxable sales it makes on February 1, 2013, or after is subject to GST/HST.
ABC Co. has until March 2, 2013, to register.