IRS Form SS-4 Instructions: Filing, Submission, and EIN Issuance

To apply for an EIN with Form SS-4, gather your entity information and responsible party details, then submit the form to the IRS online, by fax, by mail, or (for international applicants) by phone. The online application is the fastest route: most applicants finish in one session and receive the nine-digit number immediately. The IRS charges nothing for an EIN.¹

One rule to know before you start: the IRS accepts only one EIN application per responsible party per day.¹

Do You Actually Need to File Form SS-4

Not every business needs an EIN. A sole proprietor with no employees can use a personal Social Security number for federal tax purposes. Once you hire someone, form a partnership, or incorporate, that changes. The IRS also requires an EIN for these entities regardless of whether they have employees:²

Corporations and partnerships always need their own EIN.
Multi-member LLCs are treated as partnerships by default and need an EIN.
Single-member LLCs need one only if they elect corporate taxation or hire employees.
Most trusts (except certain grantor-owned revocable trusts) and all estates need one.
Tax-exempt organizations need one regardless of employee count.
Retirement plans, including Keogh plans, need one.

You also need an EIN if you file employment tax returns, excise taxes, or alcohol, tobacco, and firearms taxes.¹ Even outside those triggers, you can request one voluntarily. Many banks require an EIN to open a business account.²

What to Have Ready Before You Start

The online application session times out after 15 minutes of inactivity, so pull everything together first.

Responsible Party

Every application requires a responsible party: the individual who controls, manages, or directs the entity and its funds. For a corporation, that’s usually the principal officer. For a partnership, a general partner. For a trust, the grantor or trustee. The responsible party must be an actual person, not another entity, unless the applicant is a government body.³

You’ll enter that person’s full legal name, Social Security number or Individual Taxpayer Identification Number, and title. If the responsible party is a foreign individual with no SSN or ITIN, enter “foreign” or “N/A” on line 7b.³

Entity and Business Details

The form asks for the entity’s legal name exactly as it appears on the charter, articles of organization, or other founding document. You’ll pick the entity type (partnership, LLC, corporation, trust, and so on) and the reason for applying, whether that’s starting a new business, hiring employees, or opening a bank account.⁴

Other fields cover the date the business started or was acquired, the highest number of employees you expect in the next 12 months (broken out by agricultural, household, and other categories), and a description of the primary business activity. Trusts enter the date the trust was funded; estates enter the decedent’s date of death.³

Third-Party Designee

If you want an attorney, CPA, or enrolled agent to receive the EIN on your behalf, complete the third-party designee section on line 18. That person can answer questions about the application and receive the newly assigned number. Their authority ends once the EIN is issued, and the official confirmation notice still goes directly to the entity.³

How to Submit the Form

Four routes exist. Your options depend on where your business is located and how fast you need the number.

Online

The IRS online application is open to anyone whose principal place of business is in the United States or U.S. territories. The responsible party needs an SSN or ITIN to use it. You answer questions that mirror the paper form, and the system issues your EIN at the end of the session.¹

The tool runs Monday through Friday from 6:00 a.m. to 1:00 a.m. Eastern, Saturday from 6:00 a.m. to 9:00 p.m. Eastern, and Sunday from 6:00 p.m. to midnight Eastern.¹

Fax

Faxing the completed paper form is much faster than mailing. The IRS typically faxes back a confirmation with your EIN in about four business days. Domestic applicants (principal place of business in a U.S. state or the District of Columbia) send the form to 855-641-6935. International applicants use 855-215-1627 if faxing from within the United States, or 304-707-9471 from outside.⁵

Mail

Mailing is the slowest option. Expect about four weeks. Domestic applicants mail Form SS-4 to Internal Revenue Service, Attn: EIN Operation, Cincinnati, OH 45999. International applicants use the same address but write “Attn: EIN International Operation.”² The IRS recommends mailing at least four to five weeks before you need the number.³

Phone (International Applicants Only)

The IRS no longer issues EINs by phone to domestic applicants. If your principal place of business is outside the United States, you can call 267-941-1099 (not toll-free) Monday through Friday, 6:00 a.m. to 11:00 p.m. Eastern time. The caller must be authorized to receive the EIN and prepared to answer questions about the form, so have a completed Form SS-4 in front of you. If the representative asks, you’ll need to mail or fax the signed form within 24 hours.³

The EIN Is Free

Applying through the IRS costs nothing. Numerous third-party websites imitate the IRS application and charge anywhere from $50 to several hundred dollars for a service the IRS provides at no cost. The IRS specifically warns applicants about sites that charge for an EIN.¹ If a page is asking for payment, it isn’t irs.gov.

After Your EIN Is Issued

Online applicants can download a confirmation at the end of the session. Fax and mail applicants receive their official confirmation notice, called CP 575, through the mail after the processing period.² Keep the CP 575 somewhere safe. It’s what you’ll use to verify the number if questions come up later.

Your EIN goes on every federal tax return the entity files. You’ll also use it on W-2 forms issued to employees and 1099 forms issued to independent contractors.⁶ Most banks want the EIN and CP 575 (or other IRS documentation) to open a business account, which is one of the first steps toward keeping business and personal finances separate.

When You’ll Need a New EIN Later

An EIN stays with the entity for its life. Certain structural changes, though, mean the old entity effectively ceases to exist and a new one takes its place, requiring a fresh application. A name change, address change, or swap of the responsible party does not require a new EIN; those are updates.⁷

Common triggers by entity type:⁷

Sole proprietors need a new EIN when 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, create a subsidiary, convert to a partnership or sole proprietorship, or merge to form a new corporation. The surviving corporation in a merger keeps its existing EIN.
Partnerships need a new EIN when they incorporate, dissolve and start a new partnership, or when one partner takes over as a sole proprietor.
LLCs need a new EIN when they terminate the existing LLC and form a new corporation or partnership, or when a single-member LLC files excise or employment taxes for the first time.

1
Internal Revenue Service. Get an Employer Identification Number
2
Internal Revenue Service. Employer Identification Number
3
Internal Revenue Service. Instructions for Form SS-4 (12/2025)
4
Internal Revenue Service. Instructions for Form SS-4, Application for Employer Identification Number
5
Internal Revenue Service. Where to File Your Taxes for Form SS-4
6
Internal Revenue Service. General Instructions for Forms W-2 and W-3 (2026)
7
Internal Revenue Service. When to Get a New EIN