There are many different deductions the self-employed taxpayer can deduct. You will complete a T2125 - Statement of Business Activities and you will have a few different sections to make your deductions. These include:

• Current Expenses - items or services purchased in the tax year.
• Capital Cost Allowance or CCA - these are items of a lasting value that must be "depreciated" over time. You are only able to claim a percentage of the cost of the items.
• Motor Vehicle Expenses - claim the percentage of your total vehicle expenses which you actually used to earn income in your business.

For a complete least of eligible business expenses, see this link from CRA: https://bit.ly/2EDc2vB