The IRS allowance for mileage tax in 2014 was 56 cents per mile for business, 23.5 cents for moving or medical mileage, and 14 cents for charitable service, the IRS advises. Business rates are based on both variable and fixed costs of running a car each year.
The mileage rates for medical and moving are based only on the variable costs of running an automobile, the IRS explains. The mileage rates for 2015 are different. If a taxpayer uses a car for business purposes only, he can write off the entire expense of the car. If used for other purposes, he can only write off what he used for business reasons.