IRS Form SS-4 – Complete EIN Application Guide + Online Filing Instructions

IRS Form SS-4 – Complete EIN Application – If you’re starting a business, hiring employees, or managing an estate in the United States, obtaining an Employer Identification Number (EIN) is a crucial first step for tax compliance. IRS Form SS-4, officially known as the Application for Employer Identification Number, is the key document used to request this unique nine-digit identifier. In this comprehensive guide, we’ll walk you through everything you need to know about Form SS-4, including who needs it, how to complete it step by step, and detailed instructions for applying online. Whether you’re a sole proprietor, corporation, or non-U.S. entity, this SEO-optimized article draws from the latest official IRS resources as of 2026 to ensure accuracy and ease of use.

What is an EIN and Why Do You Need One?

An Employer Identification Number (EIN), often called a Federal Tax ID, is a nine-digit number (formatted as XX-XXXXXXX) assigned by the IRS for tax filing and reporting purposes. It’s similar to a Social Security Number but for businesses and other entities. The primary purpose of an EIN is to identify your business on tax returns, open business bank accounts, apply for business licenses, and comply with federal withholding regulations.

You might need an EIN if you’re:

  • Starting a new business.
  • Hiring employees.
  • Operating as a corporation or partnership.
  • Managing trusts, estates, or non-profits.
  • Withholding taxes on income paid to non-resident aliens.
  • Changing your business structure or acquiring an existing business.

Even sole proprietors without employees may need one for banking or certain tax filings. Without an EIN, you could face delays in business operations or IRS penalties. Note that once assigned, your EIN is permanent unless your business undergoes significant changes, and you must keep your information current using Form 8822-B for updates like address or responsible party changes.

Who Needs to File IRS Form SS-4?

Form SS-4 is required for a wide range of entities and individuals. According to the IRS, you must apply if you don’t already have an EIN but need one for any federal tax document. Here’s a breakdown:

Entity Type Examples When Required
Sole Proprietors Freelancers, independent contractors If hiring employees, opening a business bank account, or filing certain tax forms.
Corporations S-Corps, C-Corps Always, upon incorporation.
Partnerships General or limited partnerships Upon formation.
LLCs Single-member or multi-member LLCs If treated as a corporation/partnership or if electing certain tax statuses.
Estates & Trusts Decedents’ estates, revocable trusts For tax reporting on assets or income.
Non-Profits Churches, charities For exempt status and donations.
Government Entities Federal, state, or local agencies For payroll and reporting.
Others Farmers’ cooperatives, REMICs, Indian tribal enterprises As specified by IRS guidelines.

International applicants (principal business outside the U.S.) can apply but may face restrictions on online filing. If you’re unsure, check the “Do I Need an EIN?” section in the Form SS-4 instructions.

How to Apply for an EIN? (Filing Options Overview)

The IRS offers multiple ways to submit Form SS-4, with online being the fastest for eligible applicants. Here’s a quick comparison:

  • Online: Instant EIN issuance if approved; available 24/7 with limitations (see below).
  • Mail: Send completed Form SS-4 to the IRS address based on your location; processing takes 4-5 weeks.
  • Fax: Submit to (855) 641-6935 (U.S.) or (304) 707-9471 (international); response in about 4 business days.
  • Phone: For international applicants only, call (267) 941-1099 (Mon-Fri, 6 a.m.-11 p.m. ET); immediate issuance possible.

Choose based on your location and urgency. For the latest Form SS-4 (Revised December 2025), download it from the IRS website.

Step-by-Step Guide to Completing IRS Form SS-4

Form SS-4 (Rev. December 2025) has 18 lines plus sections for third-party designees. Complete it accurately to avoid delays. Use black ink if mailing/faxing, or fill digitally for online/mail. Here’s a detailed walkthrough based on the official form:

  1. Line 1: Legal Name – Enter the full legal name of the entity or individual applying.
  2. Line 2: Trade Name – If your business uses a DBA (doing business as) name, enter it here.
  3. Line 3: Care Of Name – For executors, trustees, or administrators.
  4. Lines 4a-4b: Mailing Address – Provide a complete U.S. or foreign address.
  5. Lines 5a-5b: Physical Address – If different from mailing; no P.O. boxes.
  6. Line 6: County and State – Where the principal business is located.
  7. Lines 7a-7b: Responsible Party – Name and SSN/ITIN/EIN of the person in control (e.g., owner or officer). Changes must be reported within 60 days.
  8. Lines 8a-8c: LLC Details – Check yes/no for LLC; enter member count and U.S. organization status.
  9. Lines 9a-9b: Entity Type – Select one (e.g., sole proprietor, corporation) and specify state/country of incorporation if applicable.
  10. Line 10: Reason for Applying – Check the appropriate box (e.g., started new business) and specify details.
  11. Line 11: Start Date – Month/day/year business started or acquired (e.g., 02/04/2026).
  12. Line 12: Accounting Year End – Closing month (e.g., December).
  13. Line 13: Expected Employees – Enter numbers for agricultural, household, other; use 0 if none.
  14. Line 14: Form 944 Election – Check if expecting $1,000 or less in annual employment tax liability (reinstituted as of March 2024).
  15. Line 15: First Wages Date – Month/day/year wages/annuities first paid.
  16. Line 16: Principal Activity – Check the industry (e.g., retail, manufacturing).
  17. Line 17: Principal Products/Services – Describe in detail (e.g., “Software development services”).
  18. Line 18: Prior EIN – Yes/no; if yes, provide previous EIN.

Signature Section: Sign, date, and provide contact info. For third-party designees, complete their details.

Double-check for errors, as incomplete forms are rejected. If mailing, send to: Internal Revenue Service, Attn: EIN Operation, Cincinnati, OH 45999 (U.S.); or appropriate international address.

Online EIN Application: Detailed Filing Instructions

For the quickest results, use the IRS’s online EIN Assistant if eligible. This method issues your EIN immediately upon approval and is ideal for U.S.-based businesses.

Eligibility for Online Filing

  • Principal business in the U.S. or territories.
  • Responsible party has a valid SSN or ITIN (no EIN for application).
  • Not an international applicant (use phone/fax/mail instead).

Step-by-Step Online Process

  1. Prepare Information: Gather entity details, responsible party’s SSN/ITIN, and business start date.
  2. Access the Tool: Visit the IRS EIN online application portal. Available Mon-Fri 6 a.m.-1 a.m. ET, Sat 6 a.m.-9 p.m. ET, Sun 6 p.m.-12 a.m. ET.
  3. Start Application: Answer questions mirroring Form SS-4 lines. Complete in one session—no saving allowed. Session expires after 15 minutes of inactivity.
  4. Submit: Review for accuracy and submit.
  5. Receive EIN: If approved, your EIN displays instantly. Download and print the confirmation letter.
  6. Record Keeping: Save the letter; it’s your official proof.

Tips for Success

  • Apply only once per day per responsible party.
  • For third-party applications, have signed authorization ready.
  • If errors occur, restart or use alternative methods.
  • International users in places like Indonesia: Call the international line for assistance.

After submission, use your EIN immediately for tax forms like W-9 or 941.

Common Mistakes to Avoid and Pro Tips

  • Mistake: Incomplete Responsible Party Info – Always include SSN/ITIN; omissions cause rejections.
  • Mistake: Wrong Entity Type – Double-check classifications to avoid tax issues.
  • Tip: Update Changes Promptly – Report responsible party changes within 60 days via Form 8822-B.
  • Tip: For Puerto Rico Users – Note recent replacements of certain forms (as of March 2024).
  • Pro: Check for Updates – The form was revised in December 2025; verify on IRS.gov for any 2026 changes.

Frequently Asked Questions (FAQs)

  • How long does it take to get an EIN?
    • Online: Immediate.
    • Mail: 4-5 weeks.
    • Fax: 4 days.
  • Can I apply for an EIN without a business?
    • Yes, for estates, trusts, or certain individuals.
  • What if I lose my EIN?
    • Call IRS Business & Specialty Tax Line at (800) 829-4933.
  • Is there a fee?
    • No, EIN applications are free.

Applying for an EIN via IRS Form SS-4 is straightforward with the right guidance. By following this guide, you can avoid common pitfalls and get your business tax-ready quickly. For personalized advice, consult a tax professional. Remember to use official IRS resources for the most current information, and start your application today to keep your operations compliant.