Form SS-4 applies for an EIN — the Employer Identification Number that identifies a business, trust, or estate to the IRS. It's free, and you can get the number instantly online. The two fields that matter most are the responsible party (a real person with a valid taxpayer ID, not a company) and the entity type, which has to match how the business is actually structured.
What Form SS-4 Is
Form SS-4, "Application for Employer Identification Number," gets you an EIN — a nine-digit federal tax ID for an entity rather than an individual. You need one to hire employees, open a business bank account, file business tax returns, or form a corporation, partnership, or LLC. Sole proprietors sometimes get one too, to avoid putting their SSN on W-9s and invoices.
The Responsible Party Must Be a Person
Line 7 asks for the "responsible party" — the individual who ultimately owns or controls the entity. This must be a natural person with a valid SSN, ITIN, or EIN, not another company. The IRS uses it to prevent anonymous shell entities, and naming a business here instead of a person is a frequent rejection. For most small businesses, the responsible party is the owner.
How to Fill Form SS-4
- Lines 1–6 — Entity identity. The legal name of the entity, any trade name, the mailing address, and the county/state.
- Line 7 — Responsible party. The controlling person's name and their SSN, ITIN, or EIN.
- Lines 8–9 — Entity type. Sole proprietor, partnership, corporation, LLC, trust, estate, and so on. For an LLC, note the number of members — it changes how the IRS classifies you.
- Line 10 — Reason for applying. Started a new business, hired employees, banking purpose, formed a trust, and similar.
- Sign. The responsible party or an authorized person signs and dates.
You can apply online for an immediate EIN, or by fax or mail if you prefer paper.
Is there a fee to get an EIN?
No. Applying for an EIN with Form SS-4 is completely free, whether you file online, by fax, or by mail. Third-party sites that charge to "get your EIN" are billing for a free government service you can complete yourself in minutes.
How does the EIN relate to a W-9?
Once you have an EIN, you use it as the taxpayer identification number on the W-9 forms you give to clients, instead of your personal SSN. So SS-4 comes first — it creates the business's tax ID — and that same number then flows onto every W-9, invoice, and business return you file, which is exactly the kind of detail worth entering once and reusing everywhere.