The optional standard rate allowed by the Internal Revenue Service for the business use of a car in the calendar year 2018 (January 1 through December 31, 2018) is 54.5 cents per mile.
In addition to the 54.5 cents per mile, you are also allowed to claim an expense for parking fees and tolls that are associated with the business use of your car.
The optional standard rate has some restrictions such as the number of vehicles used at one time and the prior use of certain depreciation.
An alternative to the optional standard rate per mile is to compute the business portion of the actual expenses for gasoline, repairs, insurance, depreciation, licenses, etc.
Further details about the mileage rate and other federal income tax information can be found at www.irs.gov.