If you use an automobile in your business, you may wonder how depreciation tax deductions are determined. The rules are complicated, and special limits that apply to vehicles classified as passenger autos can make it take longer than expected to fully depreciate a vehicle. First, note that if you use the “standard mileage rate” (56 cents per business mile driven for 2021), a depreciation allowance is built into the rate and you don’t need to worry about the depreciation calculations. But if you choose to use the “actual expense method” to claim deductions on a passenger auto, depreciation is calculated each year based on the car’s cost, how much you use it for business and other factors.