The ARE sole proprietorships (Schedule C, on your personal tax return), right? Not a Corporation or Partnership (or an LLC taxed as a Corporation or Partnership)?
Just to clarify James' response, you still enter 100% of the expenses for each business. But when you enter the business miles for each business, the program will automatically prorate the expenses based on the ratio of business miles for that business compared with the total odometer miles for the year.
However, depreciation may be a problem in this scenario.
If you use the Standard Milage Rate, everything will be fine (but you are required to use it for BOTH business, or NEITHER business; you can't use the Standard Mileage Rate for one business and not the other).
If you use Actual Expenses and use Straight-Line depreciation and NOT use Bonus Depreciation or Section 179, everything will be fine (but you need to do it the same for both businesses).
If you use Actual Expenses and try to use 200%DB accelerated deprecation, Bonus depreciation or Section 179, then reporting it under two different businesses will be a problem. The work-around isn't particularly easy, so you may consider going to a tax professional.
