If you use an automobile in your trade or business, you may wonder how depreciation tax deductions are determined. The rules are complicated, and special limitations that apply to vehicles classified as passenger autos (which include many pickups and SUVs) can result in it taking longer than expected to fully depreciate a vehicle. Cents-per-mile vs. actual expenses First, note that separate depreciation calculations for a passenger auto only come into play if you choose to use the actual expense method to calculate deductions. If, instead, you use the standard mileage rate (56 cents per business mile driven for 2021), a depreciation allowance is built into the rate. If you use the actual expense method to determine your allowable deductions for a passenger auto, you must make a separate depreciation...