Thanks, Hal_Al.  I'm getting hung up on the last sentence of your answer... by virtue of the IRS definition, it sounds like the home is her "principal place of business" if she uses her computer at home for bookkeeping, as the smartphone is likely mobile and not used in any regular fixed location.  That's why I'm reading the responses differently.  If I'm wrong, I'd love to know how so I can understand what I'm missing. ... View more

Hal_Al and TaxGuyBill seem to be saying different things.  By TaxGuyBill’s definition, the home is her primary place of business—even if she does not maintain a home office—and that is the test that determines whether or not mileage is deductible.  What am I missing here? ... View more