You buy an airline ticket between your home and your domicile with some extra bank $$. You check "yes" to the commuting question on the expense report so that expense will go into your taxable income. However, you end up short of travel funds and have to pay for half the airline ticket.

So, you're paying taxes on the whole ticket but you're also eating half the cost of the same ticket with a payroll deduction.

If you owed on the whole ticket, you could just not check the box for that expense since you're buying it, not Fedex. I'm curious how folks are handling the partial expenses.