What Is Form SS-4 Used For? How to Apply for an EIN

Form SS-4 is the IRS application you file to get an Employer Identification Number (EIN), the nine-digit federal tax ID assigned to businesses, trusts, estates, and other entities. The IRS issues the number for free, and once assigned it stays permanently tied to your entity. You can submit the form online, by fax, by mail, or by phone if you are applying from outside the United States.

Who Needs to File Form SS-4

Corporations, partnerships, and multi-member LLCs need an EIN whether or not they have employees. Estates and trusts that report income on Form 1041 need their own EIN, separate from any beneficiary’s Social Security Number. Nonprofits applying for tax-exempt status must have one before filing their exemption application, and the IRS starts the three-year filing clock the moment the EIN is assigned, so timing matters.¹

Hiring even one employee triggers the requirement. You cannot withhold payroll taxes, report wages, or pay federal unemployment tax without an EIN.² Household employers are in the same position. If you pay a nanny, housekeeper, or other household worker cash wages of $3,000 or more during 2026, you owe Social Security and Medicare taxes on those wages and need an EIN to report them. A separate threshold applies for federal unemployment tax: total household wages of $1,000 or more in any calendar quarter.³

Sole proprietors are the exception. If you run a business alone with no employees, you can generally use your Social Security Number for federal tax purposes. You still need an EIN if you file excise tax returns, operate a Keogh retirement plan, or are involved in a bankruptcy proceeding.⁴ Many sole proprietors get one anyway to avoid handing their SSN to every client who needs a W-9. Banks and credit unions also routinely require an EIN before opening a business account, even for some sole proprietorships.⁵

What to Have Ready Before You Fill It Out

The form is one page, but the answers set up your entity’s tax filing profile at the IRS, so it pays to get them right the first time.

Entity Name and Responsible Party

Enter the full legal name of the entity exactly as it appears on your formation documents, plus any trade name or DBA. The form then asks for a “responsible party,” which the IRS defines as the individual who ultimately owns or controls the entity and can direct its funds and assets. That person must provide their SSN or ITIN. Government entities can list an EIN for the responsible party, but everyone else has to name an actual person. If the responsible party has no SSN or ITIN and is ineligible for one, enter “foreign” or “N/A” on line 7b.⁶

Entity Type, Including the LLC Question

Line 9a asks for the type of entity. Corporations, partnerships, estates, trusts, and nonprofits each have their own box. Single-member LLCs are the tricky ones. By default, a domestic single-member LLC is treated as a “disregarded entity” for federal tax purposes, with all income and expenses flowing through to the owner’s personal return. If that describes your LLC, check the “Other” box on line 9a and write “disregarded entity.” If instead you are filing Form SS-4 specifically because you plan to elect corporate treatment on Form 8832 or S corporation status on Form 2553, check the “Corporation” box and write “single-member” along with the return you will file.⁷

You also pick a reason for applying from a list of codes: starting a new business, hiring employees, creating a trust, and so on. The IRS uses that answer to decide which returns your entity will be expected to file.

Tax Year and Employee Count

Line 12 asks for the closing month of your accounting year. Most individuals and many small businesses use a calendar year ending in December, but the rules differ by entity type. Partnerships generally must adopt the tax year used by the majority of their partners. Personal service corporations and most trusts must use a calendar year unless they qualify for an exception. Getting this wrong can cause problems when your first return is due, so check IRS Publication 538 if you are unsure.⁷

Line 13 asks how many employees you expect in the next twelve months, broken into agricultural, household, and other categories. If you expect your total employment tax liability to be $1,000 or less for the full year (roughly $5,000 or less in total wages), check line 14 to file Form 944 once a year instead of Form 941 every quarter. Skip that box and you are locked into quarterly filing.⁷

How to Submit Form SS-4

The IRS offers four ways to apply, and the speed differences are large.

Online

The online EIN assistant is the fastest option. It walks you through an interview-style questionnaire and assigns your EIN immediately when you finish. The tool is available Monday through Friday, 6:00 a.m. to 1:00 a.m. Eastern time the following day. You can apply for only one EIN per responsible party per day.⁴ Online filing is limited to entities with a principal business in the United States or a U.S. territory, and the responsible party must have a valid SSN or ITIN.

By Fax

If you cannot use the online tool, fax a completed Form SS-4. Applicants with a principal place of business in any of the 50 states or Washington, D.C. fax to 855-641-6935. Those outside the states fax to 855-215-1627 (domestic) or 304-707-9471 (international). Under the Fax-TIN program, you generally receive your EIN by return fax within four business days.⁷

By Mail

Paper applications take about four weeks. The IRS recommends mailing the form at least four to five weeks before you will need the number. The mailing address depends on whether your principal business is in the United States or abroad; current addresses are in the Form SS-4 instructions.⁶

By Phone (International Applicants Only)

If your entity has no legal residence, principal office, or place of business in the United States or its territories, you can apply by phone at 267-941-1099 (not toll-free). The line is open Monday through Friday, 6:00 a.m. to 11:00 p.m. Eastern time. The caller must be authorized to receive the EIN and answer questions about the form. Fill out Form SS-4 beforehand so the answers are in front of you. If the IRS representative requests it, mail or fax the signed form within 24 hours.⁶

Using a Third-Party Designee

You can authorize someone else, such as an accountant or attorney, to receive the EIN on your behalf by completing the third-party designee section of the form. The designee’s authority is narrow: they can answer IRS questions about the form and receive the newly assigned number, and that authority ends the moment the EIN is issued.⁶

The Application Is Free

The IRS does not charge for an EIN. Third-party websites sometimes charge to file the application for you, but you never have to pay to get one. If a site is asking for money, you are not on the IRS website.⁴

After the IRS Assigns Your EIN

You will receive a confirmation notice (CP 575) either immediately online or by mail. Keep it with your permanent business records. It is the official proof that the number belongs to your entity, and you will need it if you ever have to verify the EIN with a bank, a state agency, or the IRS.

Reporting Changes

If your business changes its mailing address, physical location, or responsible party after receiving an EIN, notify the IRS by filing Form 8822-B. Changes to the responsible party must be reported within 60 days.⁸ Skipping this step has real consequences: the IRS may send deficiency notices or demand letters to your old address, and penalties and interest keep accruing whether you receive them or not.⁹

If You Lose Your EIN

Check your original CP 575 notice, your bank account records, or any past business tax returns. If none of those work, call the IRS Business and Specialty Tax Line at 800-829-4933, Monday through Friday, 7:00 a.m. to 7:00 p.m. local time. After verifying your identity, a representative can give the number over the phone.¹⁰

Closing an EIN Account

An EIN can never be canceled or reassigned. Once issued, it belongs to that entity permanently. If you close your business, you can ask the IRS to deactivate the account by sending a letter with your entity’s legal name, EIN, address, and reason for closing. Include a copy of your original assignment notice if you still have it.¹¹¹²

1
Internal Revenue Service. Obtaining an Employer Identification Number for an Exempt Organization
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Internal Revenue Service. Businesses With Employees
3
Internal Revenue Service. Publication 926 (2026), Household Employer’s Tax Guide
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Internal Revenue Service. Get an Employer Identification Number
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U.S. Small Business Administration. Open a Business Bank Account
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Internal Revenue Service. Instructions for Form SS-4 (12/2025)
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Internal Revenue Service. Instructions for Form SS-4 (Rev. December 2025)
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Internal Revenue Service. About Form 8822-B, Change of Address or Responsible Party – Business
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Internal Revenue Service. Form 8822-B Change of Address or Responsible Party – Business
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Internal Revenue Service. Employer Identification Number
11
Internal Revenue Service. Closing a Business
12
Internal Revenue Service. If You No Longer Need Your EIN