A set rate the IRS allows for each mile driven by the taxpayer for business, charitable, medical or moving purposes. The standard mileage rate can be taken in lieu of actual expenses incurred when calculating deductible automobile expenses related to any of the four activities above. Although taxpayers have the choice of deducting either actual expenses or taking the standard mileage rate, the latter is usually chosen because it is not only simpler, but often provides a greater deduction.The standard mileage rates are based upon information compiled annually by Runzheimer International, an independent contractor to the IRS.