The IRS allows you to deduct the cost of operating your vehicle for business-related purposes. When calculating your tax bill, there are several factors that go into play: How much you drove for business purposes, how much mileage you had on your car, and the standard mileage rate. This is where we come in. We'll show you how to calculate mileage reimbursement . These three things so that next time someone asks "How much am I supposed to deduct?" You can answer without looking it up first! Determine your total business miles. Keep a record of your business miles. If you have a vehicle that is used for both personal and business purposes, keep track of the total mileage you drive on each trip. Use a mileage tracking app to track your driving habits and calculate how much gas or diesel fuel it takes to drive from point A to point B (included). Calculate how much money is being spent on gas by multiplying the number of gallons purchased ...