IRS Form SS-4

Form SS-4: Application for Employer Identification Number

A plain-English guide to IRS Form SS-4 — what it's for, who files it, when it's due, and how to complete it.

Form numberSS-4
Official nameApplication for Employer Identification Number
CategoryBusiness
Typically dueBefore you need an EIN
Official IRS Form SS-4 (PDF)

What is Form SS-4?

Form SS-4 is the application for an Employer Identification Number (EIN) — the federal tax ID a business uses to hire employees, open bank accounts and file returns.

SS-4 is the EIN application, and the fastest route is the online tool on IRS.gov, which issues the number immediately during the session. The "responsible party" line must be a real person with a taxpayer ID who controls the entity — not another company.

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Who files it

New businesses, employers, partnerships, corporations and many LLCs.

When it's due

Form SS-4 is generally due Before you need an EIN. Deadlines can move for weekends and holidays, so confirm the exact date for the current year on IRS.gov.

Key lines and parts

Here's what you'll actually fill in on Form SS-4:

  • Legal name and structure of the entity
  • Reason for applying
  • Responsible party and SSN/ITIN
  • Expected number of employees

How to file

Apply online at IRS.gov for an EIN in minutes, or submit Form SS-4 by mail or fax. It's free — avoid third-party sites that charge for it.

Common mistakes & penalties

Don't pay a third-party site for something the IRS provides free in minutes. And apply only when you're ready to use the EIN — an unused EIN attached to an entity that never files can generate confusing IRS notices down the road.
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Frequently asked questions

What is IRS Form SS-4?

Form SS-4 is the application for an Employer Identification Number (EIN) — the federal tax ID a business uses to hire employees, open bank accounts and file returns.

Who has to file Form SS-4?

New businesses, employers, partnerships, corporations and many LLCs.

When is Form SS-4 due?

Form SS-4 is generally due Before you need an EIN. Always confirm the current year's date on IRS.gov, since deadlines shift for weekends and holidays.

What's the most common mistake with Form SS-4?

Don't pay a third-party site for something the IRS provides free in minutes. And apply only when you're ready to use the EIN — an unused EIN attached to an entity that never files can generate confusing IRS notices down the road.