You'll have to make a reasonable estimate on the Fair Market Value (FMV) of your car on the date you started using it for work/business use.

One way you could get an estimate would be to use the actual purchase price less the amount you would have claimed for CCA if you had used it starting when you bought it.

As an example, if you bought the car in Oct 2020 for $29k, but didn't start using it for work until April 2021:

• $29,000 x 15% (half year rule) = $4,350 (this is the amount you could have claimed in 2020).
• $29,000 - $4,350 = $24,650 Use this figure as the cost of your "addition" for 2021.