If you use it for mostly personal use, that part isn't going to be a "business deduction" and most likely is not going to be advantageous to your situation. Depending on your past tax filings, you are most likely going to be better by doing mileage tracking and reimbursement at the IRS allowed rate and keeping the automobile personal since the majority of your travel is personal. As always, visit with your personal tax professional for guidance related to your specific situation.