If you claim unreimbursed mileage as a W-2 employee business expense, two things have to happen for it to have any impact on your tax return.
First, since it's an itemized deduction on Schedule A, you have to be able to itemize in order to take it. If your total itemized deductions don't exceed the standard deduction, then you'll get the standard and your itemized deductions won't apply.
Second, employee business expenses are a "2% misc deduction," which means the total of those deductions has to surpass 2% of adjusted gross income before you'll see the first dollar of the deduction.
These are the limitations of this type of deduction.
