The U.S. Internal Revenue Service (IRS) has opted to leave unchanged the optional standard mileage rate used to calculate the deductible costs of operating an automobile for business purposes. Beginning Jan. 1, 2012, the standard mileage rate for the use of a car, van, pickup or panel trucks is 55.5 cents per mile for business miles driven. This is unchanged from the mid-year adjustment that was made July 1, 2011. As you may recall, the IRS increased the rate from 51 cents to 55.5 cents mid-year in light of rising gas prices. The IRS normally updates mileage rates once a year.