Write down the number of miles from the vehicle's odometer before beginning your travel.
Write down the number of miles from the vehicle's odometer after travel ends.
Subtract beginning miles from ending miles to find the total number of miles traveled. For example, if the odometer said 25,000 at the beginning of the trip, and 25,100 at the end of the trip, your total miles is 25,100 - 25,000, or 100 miles.
Multiply the total number of miles by the mileage rate. For example, if total number of miles is 100 and mileage rate is 40 cents per mile, multiply 100 x 0.40 for a total reimbursement of $40.