Troubleshooting
Boxes 81, 82 & 83 on the T4 are considered self-employment income, so if you have an amount in one of those, you'll need to fill out the T2125 self-employment form.
You only need to answer basic information, such as business name and address (can be your own), industry code, and fiscal period (Jan 01 to December 31).
You don't need a business number to fill out the T2125.
