[Edited 01-23-2019]
The original answer applies to tax years prior to 2018. The tax law changes supended the deduction for non-reimbursed business expenses, and most other miscellaneous tax deductions for tax years 2018 - 2025.
Original Answer
You could claim a
deduction for the difference as an unreimbursed business expense, but you would
have to itemize your deductions in order to take the deduction.
Additionally, the deduction is allowed only for the amount that is more than 2%
of your Adjusted Gross Income (AGI).
You can claim the
mileage deduction for the business use of your vehicle. If your employer does not include the car allowance on your W-2 you would enter the
amount of reimbursement from your employer later in the interview for
Job-Related Expenses Summary. If they do report the car allowance on your W-2 you would not include it as a reimbursement from your employer. Either way, you would include the gas payments as employer reimbursement.
Since you don't have a commute, you don't have to worry about commute miles.
It is very difficult
to qualify for this deduction. That's because the expense limit is so high. In
order to qualify, your job-related expenses must be more than 2% of your AGI
(adjusted gross income).
Example: If your AGI
is $80,000, your expenses would have to be more than $1,600 ($80,000 x 2%). Even
then, you could only deduct the amount over $1,600. So, if your job-related
expenses were $3,000 you could only deduct $1,400 ($3,000 - $1,600).
