You might have missed it, but the IRS recently announced the 2010 optional standard mileage rates. These rates are typically used by businesses to help calculate mileage expenses for employees.  And just when you’ve started to remember the optional rate issued by the IRS, it changes it.

And so it has for 2010. Effective January 1, 2010, the standard mileage rate for use of a car for business miles driven will be adjusted downward to 50 cents per mile.

According to the IRS:

The new rates for business, medical and moving purposes are slightly lower than last year’s. The mileage rates for 2010 reflect generally lower transportation costs compared to a year ago.The standard mileage rate for business is based on an annual study of the fixed and variable costs of operating an automobile.

As a reminder, companies with personnel policies about their mileage reimbursement should consider updating their policies immediately to reflect this change. In the future, employers can draft a policy that states that their standard mileage rate will be consistent with the IRS’s rate without reference to a particular number.