If you use the IRS rate to substantiate the cost of business driving, the rate for 2017 will be 53.5 cents per mile (down from 54 cents per mile for 2016). The deemed depreciation rate used to reduce the vehicle’s basis is 25 cents per mile (up from 24 cents per mile in 2016). Using the IRS rate does not relieve you from substantiating the mileage, destination, purpose, and date of travel. Find details in IRS Publication 463.