I have united airlines round ticket to travel within USA...but it is likely that i will use only one way ticket to reach my destination...but won't be able to use return part of it to come back to my home city.

In this case will I be charged anything (besides what I am already charged by United) for not using return ticket? United has 150$ charges for any alterations. Will it charge me that for not using return part of the ticket?

Thanks in advance.