Kerry,What percentage of business miles vs the total can I deduct per car?
There is no such thing as a standard business use percentage. It depends on how many business miles were driven for each individual vehicle.
As I said before, you need to calculate the business miles in such a way that you would feel comfortable defending that if IRS were to ever question it.
A very commonly used method for reconstructing annual mileage is to estimate the business miles in a standard day or week and extrapolate that for the entire year based on the number of days or weeks you worked that year. This methodology is accepted by most IRS auditors.
I hate to be such a pain with this; but I can't just pull numbers and percentages out of the air for you. That is your responsibility.