When you use a vehicle for your business, there are allowable tax deductions for operating expenses incurred in operating your business.

Because your business is mobile you will be able to deduct the full cost of operating your vehicle. If you are going to use your vehicle for both personal use and business use, you will have to distribute your expenses based on your business and personal use.

Keeping Records of Business Usage
If, like many business owners, you use your vehicle for both business and private purposes, you must allocate your vehicle costs associated with the business separately from those associated with commuting or personal use. You must keep mileage records for any business travel you do. In fact, the government specifically asks you on your tax return whether you have written evidence of your vehicle expenses and is likely to deny your deduction if you don't have them.

Keep a notebook in the car and record your odometer reading. Jot down your starting and ending odometer reading for each business trip you take, as well as the reason for the trip. Most office supply stores carry notebooks designed for this purpose, in a size that's convenient for glove-box storage.

At the end of the year, you'll need to compute the total distance you drove during the year and the total distance for business. Then, you'll divide the business travel mileage by the total distance driven. The answer you get represents your percentage of business use for the year:

Business Mileage / Total Distance x 100 / 1 = % of Business Use