Not sure how much information is needed, but let’s say something comes up that requires substantial driving which the employee is willing to do with their personal car.
Beyond their wage what do you think is a reasonable approach to compensating them for the use of their car? Specifically due to depreciation, wear and tear.
If it makes a difference I’m interested in the theoretical approach rather than what I can get away with or something like that.
Make sure you are insured for this.
Do you mean that the employee has auto insurance or that I take out a policy for the employee?
You need a commercial auto policy that covers non-owned auto. The employees own policy will not cover them since they would be using their vehicle for business use.
What determines “business use”? Travel while you’re clocked into work?
Does typically not include commuting. Usually includes any trips made starting from your workplace and any following trips after that. Trip to home is usually not covered even if from last stop, so go back to workplace (covered) before going home (not covered).