IRS Form SS-4 Explained – EIN Requirements, Online Filing, and IRS Guidance

IRS Form SS-4 – In today’s business landscape, obtaining an Employer Identification Number (EIN) is a crucial step for entrepreneurs, small business owners, and organizations. Whether you’re starting a new venture, hiring employees, or managing tax obligations, Form SS-4 serves as the gateway to securing this essential identifier from the Internal Revenue Service (IRS). This comprehensive guide breaks down everything you need to know about Form SS-4, including EIN requirements, the streamlined online filing process, and key IRS guidance to ensure a smooth application. We’ll draw from official IRS resources and trusted sources to provide accurate, up-to-date information as of 2026.

What Is an Employer Identification Number (EIN)?

An EIN, often called a Federal Tax ID Number, is a nine-digit number (formatted as XX-XXXXXXX) assigned by the IRS to businesses and other entities for tax purposes. Think of it as a Social Security Number (SSN) for your business—it’s used to identify your entity on tax returns, payroll reports, and other IRS documents.

EINs are required for various business activities, such as filing employment tax returns, opening business bank accounts, applying for business licenses, or even establishing credit. Without an EIN, you may face delays in operations or compliance issues. Importantly, an EIN is free to obtain directly from the IRS, and you should avoid third-party services that charge fees for this process.

Who Needs an EIN?

Not every individual or entity requires an EIN, but many do. According to IRS guidelines, you must apply for an EIN if:

  • You operate a business with employees.
  • Your business is structured as a corporation, partnership, or multi-member LLC.
  • You withhold taxes on income paid to non-resident aliens.
  • You manage trusts, estates, or pension plans.
  • You file employment, excise, alcohol, tobacco, or firearms tax returns.
  • You’re a sole proprietor who hires employees, opens a Keogh or solo 401(k) plan, or files bankruptcy.

Sole proprietors without employees can often use their SSN for tax purposes, but obtaining an EIN is recommended for privacy and professionalism—especially when dealing with vendors or banks. Non-profits, churches, government agencies, and even household employers (like those paying nannies) may also need one.

If your business changes structure (e.g., from sole proprietorship to LLC) or you acquire an existing business, you may need a new EIN. Always check the IRS’s “Do I Need an EIN?” section in the Form SS-4 instructions for specifics.

What is Form SS-4?

Form SS-4, officially titled “Application for Employer Identification Number,” is the IRS document used to request an EIN. Revised in December 2025, this form collects details about your entity’s legal structure, responsible party, and business activities to ensure accurate assignment of your EIN.

The form is straightforward but requires precise information to avoid delays. It’s available as a fillable PDF on the IRS website, and while you can submit it via mail or fax, the online version eliminates the need for the physical form altogether. Key sections include your entity’s legal name, address, type of business, and reason for applying.

EIN Requirements: What You Need Before Applying?

Before starting your EIN application, gather the following to meet IRS requirements:

  • Legal Entity Information: Proof of your business formation, such as articles of incorporation for corporations or organization for LLCs. Form your entity with your state first to avoid issues.
  • Responsible Party Details: The name and Taxpayer Identification Number (TIN)—usually an SSN or ITIN—of the person who controls the entity’s finances and assets. This must be an individual, not a business entity (except for government applicants).
  • Business Address: A physical U.S. address (or international for foreign applicants) where the IRS can send correspondence. P.O. boxes are allowed for mailing but not as the principal business location.
  • Business Start Date and Activity Details: When your business began, its principal activity (e.g., retail, manufacturing), and employee projections.

There’s a daily limit: Only one EIN per responsible party per day across all application methods. If applying as a third-party designee, you’ll need signed authorization from the entity.

How to Apply for an EIN Online? (The Fastest Method)

The IRS strongly recommends applying online for an EIN, as it’s free, secure, and provides instant results for eligible applicants. This interview-style process mirrors Form SS-4 but is completed digitally on the IRS website.

Eligibility for Online Filing

  • Your principal business must be in the U.S. or U.S. territories.
  • The responsible party must have a valid SSN, EIN, or ITIN.
  • You’re not applying on behalf of a government entity using an EIN (use SSN/ITIN instead).

International applicants without a U.S. presence must use phone, fax, or mail.

Step-by-Step Online Application Process

  1. Visit the IRS EIN application page at IRS.gov/EIN during operating hours (Monday–Friday: 6 a.m. to 1 a.m. ET; Saturday: 6 a.m. to 9 p.m. ET; Sunday: 6 p.m. to 12 a.m. ET).
  2. Select your entity type and answer questions about your business structure, responsible party, and activities.
  3. Provide the required details, including the responsible party’s TIN.
  4. Submit the application—it must be done in one session (expires after 15 minutes of inactivity).
  5. If approved, receive your EIN immediately. Download and print the confirmation letter for your records.

Processing is instant, and you can use your EIN right away for tax filings or business setup.

Step-by-Step Guide to Filling Out Form SS-4 (For Non-Online Applications)

If online filing isn’t an option, complete the paper Form SS-4. Here’s a line-by-line breakdown based on the latest IRS instructions:

  • Line 1: Legal name of the entity (e.g., “John Doe Enterprises LLC”).
  • Line 2: Trade name or DBA if different.
  • Line 3: Care-of name for fiduciaries or designees.
  • Lines 4a–b: Mailing address.
  • Lines 5a–b: Physical street address if different.
  • Line 6: County and state of principal business.
  • Lines 7a–b: Responsible party’s name and TIN.
  • Lines 8a–c: LLC details (yes/no, member count, U.S.-organized).
  • Line 9a: Entity type (e.g., corporation, partnership; specify if “other”).
  • Line 9b: Incorporation state/country.
  • Line 10: Reason for applying (e.g., “Started new business”).
  • Line 11: Business start date.
  • Line 12: Accounting year closing month.
  • Line 13: Expected employee numbers by category.
  • Line 14: Opt-in for Form 944 if low employment taxes.
  • Line 15: First wage payment date.
  • Line 16: Principal business activity.
  • Line 17: Detailed description of products/services.
  • Line 18: Prior EIN (yes/no).
  • Third-Party Designee: Optional authorization.
  • Signature: Must be signed by an authorized person.

Enter “N/A” for inapplicable lines and ensure accuracy to prevent rejection.

Other Ways to Apply for an EIN

If online isn’t feasible:

  • Phone (International Only): Call 267-941-1099 (6 a.m.–11 p.m. ET, Mon–Fri). Provide info verbally; receive EIN immediately.
  • Fax: Send to 855-641-6935 (U.S.) or appropriate international number. Expect EIN in 4 business days.
  • Mail: Send to IRS EIN Operation in Cincinnati, OH. Allow 4–5 weeks.

Use only one method to avoid duplicates.

IRS Guidance and Tips for Success

The IRS provides extensive resources, including Publications 15, 51, and 80 for employer tax guides. Key tips:

  • Update changes (e.g., address, responsible party) via Form 8822-B within 60 days.
  • For LLCs, understand tax classification defaults or elect via Form 8832.
  • Avoid common errors like mismatched names or incomplete lines.
  • If you lose your EIN, check old tax returns or contact the IRS at 800-829-4933.

Certain entities may also need to report beneficial ownership to FinCEN.

Common Mistakes to Avoid When Applying for an EIN

  • Using an entity’s EIN instead of an individual’s TIN as the responsible party.
  • Applying multiple times or via multiple methods.
  • Forgetting to form your legal entity first.
  • Providing inaccurate business activity descriptions.
  • Ignoring the one-EIN-per-day limit.

Frequently Asked Questions (FAQs)

How long does it take to get an EIN?

  • Online: Instant.
  • Fax: 4 business days.
  • Mail: 4–5 weeks.

Can I apply for an EIN before my business starts?

Yes, but provide an estimated start date on the application.

Is there a fee for an EIN?

No, it’s free from the IRS. Beware of scams.

What if I already have an EIN?

Use Line 18 to disclose it; you may not need a new one unless circumstances change.

Can non-U.S. residents get an EIN?

Yes, via phone, fax, or mail.

Securing an EIN via Form SS-4 is a foundational step for any business aiming for compliance and growth. By understanding the requirements, leveraging online filing, and following IRS guidance, you can obtain your EIN efficiently. For personalized advice, consult a tax professional or visit IRS.gov for the latest updates. Start your application today and set your business up for success.