As a business owner or self-employed individual, you can enter either the standard mileage rate or the actual cost method, which tracks what you paid for gas and maintenance.
To use the standard mileage rate, you must keep a log of each trip with miles driven during the first year your vehicle is used for business. After that, you can either go with standard mileage or actual cost (unless you lease, in which case you must stick with standard mileage for the duration of the lease).
To enter vehicle related expenses:
The vehicle expenses have a series of questions and you can choose to use either a cost per mile or use the actual costs for the vehicle (including gas) and the next page has tolls and parking. There are more expense categories on the Add Expenses page if you click on the blue triangle next to Less Common Expensesfor legal and professional fees, commissions and much more.
In the Self-Employed Turbo Tax version with the Business tab at the top
click here for more tax tips for drivers