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How to treat miles driven to the mechanic, gas station, etc when calculating business use of car?
Alright, IRS Publication 463: Travel, Entertainment, Gift, and Car Expenses Business and personal use. If you use your   car for both business and personal purposes,   you must divide your expenses between business   and personal use. You can divide your expense   based on the miles driven for each purpose. Example. You are a sales representative   for a clothing firm and drive your car 20,000   miles during the year: 12,000 miles for business   and 8,000 miles for personal use. You can   claim only 60% (12,000 ÷ 20,000) of the cost of   operating your car as a business expense Obviously nothing helpful in the code.  So I would use option 1, weight the maintenance-related mileage by the proportion of business use.  Although if you use your car for business a lot (and perhaps have a spouse with a car), an argument could be made for 3.  So I would consider my odds of being audited (even lower this year due to IRS budget cuts) and choose 1 or 3. And of course never throw anything away until you're room temperature.