This is something I should have been doing all along, and I'm not sure why I didn't think of it sooner since it isn't a difficult calculation. I will take the total miles driven and multiply it by the depreciation factor below.
Here's how I calculated the depreciation factor:
- Cost of 2009 Pontiac G5: $13,000
- Expected Life of Car: 150,000 miles
- Cost per mile: $.0867
I drove 6,250 miles in April, a bit more than average since I don't drive to Omaha every month!
6,250 * $.0867 = $541.88
I will also make an adjustment to the value of my car in Quicken. Previously I had written down its value by $3,000. Based on the above calculation, I overestimated the depreciation. Since I ended April with 18,860 miles on my car, I will deduct $1,093.29 from the original purchase price for usage prior to March. Moving forward I will make a monthly adjustment.