Record the total number of kilometres driven from Jan. 1 to Dec. 31 and calculate the number of kilometres you have driven for business reasons, recording the date, destination and reason for each trip. For example, if you have driven a total of 10,000 kilometres in a year and you have calculated that 1,000 kilometres were for business, you can claim a 10% deduction for the use of your car, Trépanier says.