You are mixing apples and oranges: the mileage rate on the IRS website is the tax deduction you may take for mileage, if not reimbursed for it. It is not the rate at which an employer is required to reimburse mileage and has nothing to do with actual reimbursement, which may be more, less, or the same. Indeed, an employer has NO legal obligation to reimburse mileage at all: it would be legal to make employees absorb their own mileage costs. So your employer may reimburse you only $0.45 per mile if it chooses. Speak to your tax preparer, howeve: possibly, you may be able to also get some tax deduction for the difference between the IRS rate and the rate you are actually reimbursed.