How does one calculate "Total Interest Paid On Vehicle" for business?

How do I calculate "Total Interest Paid On Vehicle" for business use? Turbotax gives a good explanation of WHEN to claim the "Total Interest Paid On Vehicle" but does not tell you HOW to do so. Is this deduction just for those who are leasing or still paying off their vehicle??? I read on cars direct (2016), "You need to calculate the entire expenditures of your car. Multiply your monthly fee by 12 to get the exact dollar amount. If you have had your car for less than 12 months, calculate the expense by multiplying your monthly fee by the number of months you have leased the vehicle or car...  Deducting the costs of leasing a car is ideal for those who use any vehicle for 50% or more business-related reasons." I've also read it's important to take into account the extra costs, including gas, insurance, and maintenance fees. Thus, if my car is paid off, can I still use this deduction?

 

Any insight would be appreciated! ðŸ˜‰

 

Pop-up info offered on Turbotax:

"If you used this vehicle the entire year or kept mileage records even when you weren't using it for business, enter the total amount of interest paid on this vehicle for 2019 and we will figure the amount that is deductible for this business.

If you did not use this vehicle for the entire year and entered months of business use, still enter the total amount of interest paid in 2019."