You can deduct actual mileage costs when you use your car for business purposes. as a general rule, you must keep a diary that includes the beginning and ending odometer readings foreach trip, as well as the trip’s purpose. Loophole: The diary entry is sufficient to prove your deduction if you are taking the IRS standard mileage rate for driving costs. You don’t need to collect receipts for gasoline, repairs, insurance and other automobile expenses unless you’re deducting your actual driving expenses rather than the IRS rate.