I entered my biz mileage as a deduction, but my fed amount due did not go down; why?

[AnnetteB]

If you receive a W-2 for your work, then your unreimbursed employee expenses, such as your business miles, are deducted on Form 2106 as Employee Business Expenses. 

These expenses are then included on Schedule A Itemized Deductions as a part of the deductions limited by 2% of your adjusted gross income.  So, be aware that unless you are itemizing deductions, including the employee business expenses may not affect your refund/balance due.  

Keep reading for more information, including how to add these expenses to your return.

https://ttlc.intuit.com/replies/4800418

(If you were asking about entering expenses as a self-employed person, please use the search term “business expenses” as described above to go to that section of your return.)