Form SS-4 — Application for Employer Identification Number (EIN)
Form SS-4 is used to apply for an Employer Identification Number (EIN) — the business equivalent of a Social Security Number. An EIN is required for any entity that has employees, files business tax returns, opens a business bank account, or applies for business licenses. For tax professionals, Form SS-4 is a foundational form for new business clients — and the responsible party designation on the form has significant legal and tax implications.
Key Rules and Authority
| Rule | Detail |
|---|---|
| Online EIN | Immediate — irs.gov/ein |
| Fax EIN | 4 business days |
| Mail EIN | 4–5 weeks |
| Responsible Party | Must be an individual — not an entity |
| EIN for Trust | Required for irrevocable trusts |
| EIN for Estate | Required when estate has income |
When an EIN Is Required
An EIN is required for: (1) any entity with employees; (2) corporations, partnerships, and LLCs (regardless of employees); (3) trusts (irrevocable trusts, grantor trusts with a third-party trustee); (4) estates with income; (5) retirement plans (401(k), SEP-IRA, SIMPLE IRA); (6) entities that file employment, excise, or alcohol/tobacco/firearms tax returns; and (7) entities that withhold taxes on income paid to non-resident aliens. Sole proprietors without employees can use their SSN instead of an EIN, but many choose to obtain an EIN to protect their SSN from disclosure on 1099 forms.
Frequently Asked Questions
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