Is it too late to form an LLC for 2017's tax year?

Yes, if you operate on a calendar year, that is from 1/1 until 12/31, of any year. If you choose to operate on a fiscal year, see below.

You must figure your taxable income on the basis of a tax year. A “tax year” is an annual accounting period for keeping records and reporting income and expenses. An annual accounting period does not include a short tax year. The tax years you can use are:

• Calendar year - 12 consecutive months beginning January 1 and ending December 31.
• Fiscal year - 12 consecutive months ending on the last day of any month except December. A 52-53-week tax year is a fiscal tax year that varies from 52 to 53 weeks but does not have to end on the last day of a month.

Unless you have a required tax year, you adopt a tax year by filing your first income tax return using that tax year. A required tax year is a tax year required under the Internal Revenue Code and the Income Tax Regulations. You have not adopted a tax year if you merely did any of the following.

• Filed an application for an extension of time to file an income tax return.
• Filed an application for an employer identification number.
• Paid estimated taxes for that tax year. 

If you file your first tax return using the calendar tax year and you later begin business as a sole proprietor, become a partner in a partnership, or become a shareholder in an S corporation, you must continue to use the calendar year unless you get IRS approval to change it or meet one of the exceptions listed in the instructions to Form 1128, Application To Adopt, Change, or Retain a Tax Year (PDF).

Generally, anyone can adopt the calendar year. However, if any of the following apply, you must adopt the calendar year.

• You keep no books or records;
• You have no annual accounting period;
• Your present tax year does not qualify as a fiscal year; or
• You are required to use a calendar year by a provision of the Internal Revenue Code or the Income Tax Regulations.

A short tax year is a tax year of less than 12 months. A short period tax return may be required when you (as a taxable entity):

• Are not in existence for an entire tax year, or
• Change your accounting period.

Tax on a short period tax return is figured differently for each situation.

Even if you (a taxable entity) were not in existence for the entire year, a tax return is required for the time you were in existence. Requirements for filing the return and figuring the tax are generally the same as the requirements for a return for a full tax year (12 months) ending on the last day of the short tax year.

For more information, see Publication 538, Accounting Periods and Methods (PDF).

Once you have adopted your tax year, you may have to get IRS approval to change it.  To get approval, you must file Form 1128 (PDF).  See the instructions for Form 1128 for exceptions. If you qualify for an automatic approval request, a user fee is not required. If you do not qualify for automatic approval, a ruling must be requested and a user fee is required. See the instructions for Form 1128 for information about user fees if you are requesting a ruling