I opened an LLC in 2017, but am not using it for ay business until 2018. No bank accounts yet or anything. Do I need to file a 2017 return?

[Critter]

Is the LLC incorporated or a partnership ?

[johnboy11a]

Sole Proprietorship LLC

[JulieH1]

Yes.

 Since you have an IRS-issued federal tax ID, you are in their system and the IRS will be expecting you to file an income tax return for 2017

An LLC can also be taxed as a corporation (either a regular corporation or an S Corporation), provided the proper paperwork is filed with the IRS. If that's the case, then the LLC should file Form 1120 or Form 1120S by March 15, 2018, or file an extension on Form 7004, giving the LLC until September 17, 2018 to file the 1120 or 1120S. 

Bottom line: even a business with no profit should prepare and file a return. Otherwise, the business could be subject to the late filing penalties, which can add up!