Car loan interest deduction for rideshare driver

[Mojavejava]

This question pertains to our 2018 tax return. We got a car title loan on our car in the fall of 2017. In July 2018 we started using the car to drive for Uber and Lyft. It is my understanding that the portion of the car loan interest that corresponds to the mileage used for business is tax deductible on our Schedule C even if we take the standard mileage deduction. But do we start calculating the business use % beginning in January or in July when we started using the car for Uber/Lyft? Am I correct in assuming the business use % is based on miles and not time (days, hours, weeks, months)? But I still need to know whether to calculate the % of business miles beginning in January or July.

Many thanks for any help!

[VictorW9]

You started driving for Uber and Lyft in July. So, that is when you should begin apportioning. The first half of the year, the vehicle was used more for personal use and has no effect on your taxes.

[Mojavejava]

Many thanks! So does that mean when completing the mileage section, I omit my personal and commuting miles prior to July given that the vehicle wasn't used for business until July?

[KatrinaB48]

Yes, the mileage before you used your car for business use does not relate to your schedule c.