Yes, you do! But please don't stop reading. There are important things you need to know about keeping track of your business mileage. If you have a vehicle you own personally but also use for business, you must keep a vehicle expense logbook (also known as a mileage book).  Why a Mileage Book is Important You can only deduct vehicle expenses for the portion of expenses that relate to your business.  Keeping track of all your trips (both personal and business) is the only way to know how to split vehicle costs (such as fuel, insurance, repairs, and maintenance) between business [...]