What is EIN (Employer Identification Number)?

The EIN (Employer Identification Number) is the federal tax ID for every US business entity. It functions like a Social Security Number (SSN) for businesses, used on all IRS filings, W-2s, 1099s, and business bank accounts.

**Who must have an EIN**

- All C-corporations and S-corporations - All multi-member LLCs (taxed as partnerships) - Any entity with employees - Trusts and estates - Single-member LLCs with employees or excise tax obligations

Single-member LLCs without employees can use the owner's SSN, but most open a business bank account immediately and get an EIN anyway — banks require it, it keeps business and personal finances separate, and it protects your SSN from being shared with clients who issue 1099s.

**Applying for an EIN**

The IRS issues EINs free via the online EIN Assistant at IRS.gov. The process takes under 10 minutes and the EIN is issued immediately upon completion. You must have a valid SSN or ITIN as the 'responsible party' (the person who controls the entity). Non-US residents without an SSN must apply by mail or fax (Form SS-4), which takes 4-6 weeks.

Once issued, the EIN cannot be cancelled or reassigned, but it can be inactivated. If you dissolve a business, the EIN is retired but never reused.

**EIN format**

An EIN is formatted as XX-XXXXXXX (two digits, hyphen, seven digits). It must appear on all federal tax returns (Form 1120, 1120-S, 1065), on W-2s issued to employees, on 1099-NECs issued to contractors, on Form W-9 when collected by clients, and on corporate bank account applications.

**State tax IDs**

Most states have their own business tax registration and may issue a separate state EIN or state employer account number for payroll withholding. These are distinct from the federal EIN and typically obtained after registering with the state's department of revenue or labor department.