But OP has only one client. Since he goes to the same location every day, isn't that commuting, since the actual work is being done at the client's location?

Not if he has a qualified office in the home ... read the rules ... they changed a few years back to allow for administrative functions to qualify.

"I bill my travel time." You bill for the time to get there, or for the mileage?

For a Sch C filer they can add anything they want to a client's invoice and call it anything they want.  Some people add a  mileage charge or some  add travel time ... doesn't matter as long as the  client is will to pay the charge/bill.  

Right, but an expense reimbursement isn't taxable, right?

You are thinking employee ... the poster is self employed.  All billed income is reported on the Sch C and then any expenses can be deducted from the income.  So if the income is increased by a "mileage allowance" that is billed to the client then the mileage expense can be deducted as an expense.   Same thing if the business owner takes a job out of town for a customer and adds travel costs to the billing invoice ... then the travel expenses can be deducted on the Sch C.  Basically an IN & OUT transaction on the Sch C.

If you have a verified home office then all business mileage is deducible from the moment you leave your door.  But if you ONLY have one client  then it would seem like you should be an employee not a sub contractor. 

You can take the office in home expenses if you meet the "regularly" and "exclusively" tests.

To deduct expenses related to the business use of part of your home, you must meet specific requirements. Even then, your deduction may be limited. 

General Rules

To qualify to claim expenses for business use of your home, you must meet the following tests. 

1. Your use of the business part of your home must be: 
------a. Exclusive (see below), 
------b. Regular, 
------c. For your trade or business, AND 

2. The business part of your home must be one of the following: 
------a. Your principal place of business
------b. A place where you meet or deal with patients, clients, or customers in the normal course of your trade or business, or
------c. A separate structure (not attached to your home) you use in connection with your trade or business. 

Additional Rules For Employees

There are additional tests for employee use. If you are an employee and you use a part of your home for business, you must meet the tests discussed above plus: 

1. Your business use must be for the convenience of your employer, and 
2. You do not rent any part of your home to your employer and use the rented portion to perform services as an employee. 

Whether the business use of your home is for your employer's convenience depends on all the facts and circumstances. However, business use is not considered to be for your employer's convenience merely because it is appropriate and helpful. Also, if your employer provides you with office space at the employer's location, it is very difficult to support that working at home is for the employer's convenience.

Exclusive Use:  To qualify under the exclusive use test, you must use a specific area of your home only for your trade or business. The area used for business can be a room or other separately identifiable space. The space does not need to be marked off by a permanent partition. 

You do not meet the requirements of the exclusive use test if you use the area in question both for business and for personal purposes.

Where to Report:

This article discusses where to deduct it in Turbotax:   https://turbotax.intuit.com/support/iq/Deductions---Credits/Can-I-take-the-Home-Office-Deduction-/GE...

Thank you for your response, but my question was not answered.  I didn't ask if my home office was my principle place of business.  As I stated in my question, it is.  The amount of clients I have has nothing to do with whether I am an employee or IC.  I am an IC, there is nothing from me taking on other clients.  I do have other clients BTW.  My question IS I am driving to my main clients office 4x a week from my home office, is this considered a deductible expense or commuting?  This seems to be a gray area as I am driving to the same clients office from my home office almost daily.

Ok ... read the form 8829 instructions for your answer on what is a principle place of business  ... <a rel="nofollow" target="_blank" href="https://www.irs.gov/pub/irs-pdf/i8829.pdf">https://www.irs.gov/pub/irs-pdf/i8829.pdf</a>