Choosing a Business Entity Structure: EIN Rules and Tax Elections

Your choice of business entity structure and EIN requirements are tied together at the federal level: the IRS won’t issue an Employer Identification Number until you can tell it what kind of entity you’re forming, and the structure you pick decides how your income is taxed, which returns you file, and whether an EIN is required at all.¹

How Each Structure Is Taxed and Whether It Needs an EIN

The IRS classifies businesses by legal organization, not by name or industry. Five structures cover almost everyone:

Sole proprietorship. You and the business are the same taxpayer. Income and expenses go on Schedule C of your personal return. Most sole proprietors can operate on their Social Security number alone.²
Partnership. Two or more people carrying on a business together. The partnership files Form 1065 as an informational return, and profits and losses pass through to each partner’s personal return. Every partnership needs its own EIN.³
Limited liability company. The IRS has no dedicated tax classification for LLCs. A single-member LLC is treated as a sole proprietorship by default; a multi-member LLC is treated as a partnership. Either can elect corporate treatment instead.⁴
C corporation. A separate taxable entity. The corporation pays income tax on profits, and shareholders pay tax again on dividends. Every corporation needs an EIN.
S corporation. A corporation that elects pass-through treatment, avoiding the double-tax layer. To qualify it must be a domestic corporation with no more than 100 shareholders, only one class of stock, and no shareholders that are partnerships, other corporations, or nonresident aliens.⁵

Every entity that applies for an EIN must name a responsible party: the individual who controls or directs the business and its funds. That person’s Social Security number or ITIN goes on the application, and the IRS treats them as the primary contact.

Which Entities Are Required to Have an EIN

All corporations and partnerships must have an EIN. So must any business, regardless of structure, that hires employees, maintains a retirement plan, or files excise tax returns.¹

A sole proprietor or single-member LLC with no employees and no excise tax obligations can technically use just the owner’s Social Security number. Most still get an EIN. Banks generally require one to open a business checking account, and putting an EIN rather than an SSN on invoices and vendor forms reduces identity-theft exposure. The moment you hire an employee or elect corporate treatment, the EIN stops being optional.

Trusts and estates have their own rules. An irrevocable trust needs its own EIN, as does an estate that continues to operate a business after the owner’s death. A revocable trust that becomes irrevocable when the grantor dies needs a new EIN at that point. A change in trustee name or address does not trigger a new number.⁶

Choosing Tax Treatment for an LLC

Because the LLC has no default federal tax category of its own, owners who want treatment other than the default file an election. Two forms handle the possibilities, and each has its own deadline.

Form 8832 to Change the Default Classification

A single-member LLC is disregarded by default; a multi-member LLC is a partnership by default. To be taxed as a C corporation instead, the LLC files Form 8832. The effective date can’t be more than 75 days before the filing date and can’t be more than 12 months after it.⁷

Once you make a classification change through Form 8832, you’re generally locked in for 60 months. Newly formed entities that elected on the date of formation are the exception and can change again without waiting. Missed the window? Late-election relief may be available within three years and 75 days of the intended effective date, if you can show reasonable cause.⁷

Form 2553 for S Corporation Status

An LLC that wants S corporation treatment takes two steps: it must first be eligible for corporate classification (by default or through Form 8832), then file Form 2553 to make the S election. The filing deadline is no later than two months and 15 days after the beginning of the tax year the election should take effect, or at any point during the preceding tax year.⁸

Missing the Form 2553 deadline is a common mistake, and it usually pushes S-corp treatment out to the next tax year. Relief is sometimes available, but planning around it is a poor substitute for filing on time.

Form the Entity at the State Level First

The IRS expects your LLC, corporation, or partnership to exist under state law before you apply for an EIN. If you haven’t filed your articles of organization or incorporation with the secretary of state, the EIN application can be delayed.¹

State filing fees vary. Some states charge under $50; others charge several hundred dollars, and a handful require additional steps such as newspaper publication. These costs are separate from the EIN application, which is free. Most states also require periodic reports to keep the entity in good standing, with penalties for late filing that can go as far as administrative dissolution. A state income tax return does not satisfy the annual report requirement — they are separate obligations.

What the EIN Application Asks For

Form SS-4 is the EIN application. It’s short but unforgiving about inaccuracy.⁹ You provide:

The legal name registered with your state (marketing or DBA names go on a separate line).
The entity type, matching what you formed at the state level.
The responsible party’s name and Social Security number or ITIN.
The reason for applying — new business, hiring employees, opening a bank account, or another listed reason.
A description of the business activity and the products or services sold.
The physical business location, plus a mailing address if different.

You can authorize a third-party designee to receive the EIN for you. That authority ends as soon as the number is assigned; it doesn’t cover ongoing tax matters. If the designee’s address matches the taxpayer’s address, the application has to be submitted by mail or fax rather than online.¹⁰

How to Submit

Three submission methods, very different timelines. The online application through the IRS website is the fastest: it issues the EIN immediately on approval, is free, and runs Monday through Friday, 6:00 a.m. to 1:00 a.m. Eastern time. Each responsible party can obtain only one EIN per day through the online system.¹ Fax submission of a signed Form SS-4 takes about five business days, with the IRS faxing the EIN back to the number on the form.¹¹ Mail submission takes roughly 30 days, so apply four to five weeks before you need the number.¹⁰

When a Structural Change Requires a New EIN

An EIN belongs to a specific entity structure. If that structure fundamentally changes, the old number no longer applies.

Sole proprietors need a new EIN if they incorporate, form a partnership, or file for bankruptcy. Corporations need a new EIN when they receive a new charter from the secretary of state, become a subsidiary of another corporation, merge to create a new entity, or convert to a partnership or sole proprietorship.⁶ Partnerships need a new number if one partner takes over and runs the business as a sole proprietorship, or if the partnership dissolves and a new one forms.

Plenty of changes don’t require a new EIN. Moving offices, changing a trade name, switching a registered agent, or updating the name or address of a trustee, officer, or partner are all administrative updates. You notify the IRS through the appropriate form or letter and keep the existing number.⁶

Consequences of Operating Without a Required EIN

Skipping the EIN when you’re required to have one has financial teeth. When a business fails to give a correct taxpayer identification number to a bank, client, or other payer, that payer must withhold 24 percent of reportable payments. This backup withholding applies automatically. The money is credited against your taxes eventually, but until then you’ve lost nearly a quarter of your cash flow.¹²

Separately, the IRS can impose a $50 penalty for each failure to include a correct taxpayer identification number on a return, statement, or other required document, capped at $100,000 per calendar year.¹³ The penalty doesn’t apply if you can show the failure was due to reasonable cause rather than willful neglect, but a free ten-minute online application is a hard thing to explain your way around.

1
Internal Revenue Service. Get an Employer Identification Number
2
Internal Revenue Service. Topic No. 407, Business Income
3
Internal Revenue Service. Publication 541, Partnerships
4
Internal Revenue Service. Limited Liability Company (LLC)
5
Internal Revenue Service. S Corporations
6
Internal Revenue Service. When to Get a New EIN
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Internal Revenue Service. Form 8832, Entity Classification Election
8
Internal Revenue Service. About Form 2553, Election by a Small Business Corporation
9
Internal Revenue Service. About Form SS-4, Application for Employer Identification Number (EIN)
10
Internal Revenue Service. Instructions for Form SS-4
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Internal Revenue Service. Processing Status for Tax Forms
12
Internal Revenue Service. Backup Withholding
13
eCFR. 26 CFR 301.6723-1 – Failure to Comply With Other Information Reporting Requirements