What is the proper way to substantiate unreimbursed business mileage expenses?

If you drive your vehicle for work, but your employer does not reimburse you for this expense, you may deduct this as an unreimbursed business expense.  You will report this deduction on Schedule A.  However, for the IRS to accept it as a valid deduction, you must keep good, contemporaneous records, including: (1) a mileage log showing the odometer reading at the beginning and end of the year, (2) a log of the mileage driven for each business use (this can be in a log book or calendar) and (3) the business purpose of each trip, including address and activity taken.  The best way to prepare this for the IRS is to create a spreadsheet with the columns showing (1) date of trip, (2) destination address (3) mileage and (4) business purpose (be specific).  Remember that you cannot count mileage from home to work or other destination unless you work from your home office. These requirements are set out in IRS Code Sec. 274(d).