What Is Form SS-4 Used For? Filing, Submission, and CP 575

Form SS-4 is the IRS application used to request an Employer Identification Number, the nine-digit federal tax ID assigned to businesses, nonprofits, estates, trusts, and other entities that aren’t individuals. The EIN works like a Social Security number for the organization: it ties every tax return, payroll deposit, and information filing back to the right entity, and it stays with that entity permanently even if the name or address changes.¹ Applying costs nothing, and the IRS warns against sites that charge a fee for the service.²

Who Files Form SS-4

Corporations, partnerships, and multi-member LLCs need an EIN to file federal returns and report income shared among owners. Estates handling a decedent’s assets, trusts distributing income to beneficiaries, nonprofits seeking tax-exempt status, and farmers’ cooperatives all need their own numbers as well.³ The underlying rule is that any entity that isn’t an individual person uses an EIN rather than a Social Security number for federal tax purposes.⁴

Sole proprietors sit in a gray area. If you run a one-person business with no employees, no Keogh retirement plan, and no obligation to file excise tax returns, you can generally use your Social Security number and skip Form SS-4. The moment you hire your first employee, open a Keogh plan, or need to file employment or excise tax returns, you need an EIN.¹ Many solo owners get an EIN anyway to avoid handing their Social Security number to clients and vendors, but that’s a privacy choice, not a legal requirement.

What the Form Asks For

The current version of Form SS-4 is free at IRS.gov. It runs 18 numbered items, most of them short.

Legal name and trade name. Enter the entity’s exact legal name as it appears on the organizing documents, such as articles of incorporation or a trust agreement. Any “doing business as” name goes on the separate trade name line. The legal name matters more than it looks. The IRS builds a “name control” from what you put on SS-4, and every future e-filed return is matched against it. A mismatch triggers a rejection.⁵

Responsible party. This is the individual who ultimately owns or controls the entity. For a corporation, typically the principal officer. For a partnership, a general partner. For a trust, the grantor or trustee. For an estate, the executor or administrator. The responsible party must give their own Social Security number, ITIN, or existing EIN.³⁴

Entity type and reason for applying. You check a box for the type of organization and indicate why you need the number: starting a new business, hiring employees, creating a trust, and so on.

Expected employees. If you expect employees, enter the anticipated headcount and the date wages will first be paid.³

How to Submit It and How Long It Takes

Online, Issued Immediately

The fastest route is the IRS online EIN application, which issues the number on approval. The tool is available Monday through Friday from 6:00 a.m. to 1:00 a.m. the next day, Saturday from 6:00 a.m. to 9:00 p.m., and Sunday from 6:00 p.m. to midnight, all Eastern time.² The online option is only open to applicants whose principal place of business is in the United States or U.S. territories.⁶

Fax, About Four Business Days

Under the IRS Fax-TIN program, a completed Form SS-4 sent by fax comes back with an EIN in about four business days. The domestic fax number is 855-215-1627. International applicants use 304-707-9471.⁶

Mail, About Four Weeks

Mailing the form takes the longest. Expect roughly four weeks before the EIN arrives.³

International Applicants

If your principal place of business is outside the United States, the online tool is unavailable. You can call 267-941-1099 Monday through Friday, 6:00 a.m. to 11:00 p.m. Eastern time, or submit the form by fax or mail to the IRS international operation in Cincinnati, Ohio.⁶

One EIN Per Responsible Party Per Day

The IRS limits EIN issuances to one per responsible party per day. If you’re forming several entities at once with yourself listed as the responsible party on each, the applications have to be spread across separate days. For trusts, the cap applies to the grantor or trustor; for estates, to the decedent or debtor. It applies whether you file online, by phone, by fax, or by mail.⁷

The CP 575 Confirmation Notice

After the IRS processes the application, it mails a CP 575 notice to the entity’s registered address. That notice is the official confirmation of the EIN assignment and lists the entity’s legal name, address, EIN, and the federal tax forms it’s required to file. Keep it with your permanent records. Banks, lenders, and government agencies routinely ask for it when you open accounts, apply for licenses, or bid on contracts.

Online applicants can download and print a confirmation immediately, and the CP 575 still arrives by mail afterward. If you lose the notice, the IRS won’t reissue it, but you can request a Letter 147-C as replacement verification.²

Keeping the Information Current

The EIN itself stays the same for the life of the entity, but the information attached to it can change. If the business moves or the mailing address changes, notify the IRS using Form 8822-B. The same form covers changes to the responsible party, and that change carries a stricter deadline: file Form 8822-B within 60 days of the new responsible party taking over.⁸

Missing the responsible-party update is where many businesses quietly fall out of compliance. A founder leaves, a new partner takes control, no one files the form, and the IRS is left trying to reach a person who no longer runs the entity.

1
Internal Revenue Service. About Form SS-4, Application for Employer Identification Number (EIN)
2
Internal Revenue Service. Get an Employer Identification Number
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Internal Revenue Service. Instructions for Form SS-4 (12/2025)
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eCFR. 26 CFR 301.6109-1 – Identifying Numbers
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Internal Revenue Service. Using the Correct Name Control in E-Filing Partnership Tax Returns
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Internal Revenue Service. Employer Identification Number
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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