Vehicle purchased in Oct 2017 for $29k, but did not start using of work until April 2018, and only have a Fair Market Value of $17k done in Mar 2019. How do I determine FMV for April 2018?
You'll have to make a reasonable estimate on the Fair Market Value (FMV) of your vehicle on the date you started using it for Business or Employment use (April 2018).
One way you could get a fairly accurate calculation would be to use the actual purchase price - minus - the amount you would have claimed for CCA if you had used it starting on the purchase date.
So $29,000 x 15% (half year rule) = $4,350 (this is the amount you could have claimed)
29,000 - 4,350 = $24,650 Use this figure as the cost of your "addition". If you were questioned by CRA as to how you came up with this figure, you would be able to show them you used this method of calculation and considered it to be reasonable.