I use one car in two different sole proprietorships, so the answer to the TurboTax question: "When did you start using this vehicle for work" is different for each, okay?

[LoveableMusician]

The businesses are in separate industries, music performance and project management.

[tygrtchr]

Since you have two separate businesses, you will work on each one (income and deductions) separately.  Make sure you have meticulous records about mileage and the purpose of each trip.  If the car is also used for commuting to a job and personal care, it would probably be best if you take the standard per mile deduction. Put the "business miles" travelled in one business and then close it out.  When you start working on the second business, you will do the same thing.  We have had something similar on our taxes in the past and this worked best for us.