EIN (Employer Identification Number)

An Employer Identification Number (EIN), also called a Federal Tax Identification Number, is a nine-digit number formatted as XX-XXXXXXX that the IRS assigns to a business entity for federal tax purposes. It is the entity equivalent of a Social Security Number and is the foundational tax ID on every US payroll filing, 1099 information return, 1042 withholding return and corporate income tax return. The IRS issues EINs free of charge, per the official Apply for an Employer Identification Number (EIN) online page. Application is via Form SS-4, with full instructions on the IRS About Form SS-4 page.

How an EIN Works

An EIN identifies a single legal entity. The IRS uses the EIN to track:

• Federal employment tax filings (Form 941 quarterly returns, Form 940 federal unemployment, W-2 wage statements)
• Federal income tax returns for the entity itself (Form 1120, 1120-S, 1065, 990)
• Information returns issued by the entity (Form 1099 series, Form 1042 and 1042-S)
• Federal excise tax filings
• Employee benefit plan filings (Form 5500)

Once an EIN is issued, it travels with the entity for its entire life. A change of business name, additional locations, or new lines of business do not require a new EIN. A change of legal structure, however (for example, a sole proprietor incorporating, or two corporations merging into a new entity), generally does require a new EIN. The full list of “do you need a new EIN” scenarios is published on the IRS Do You Need a New EIN page.

Who Needs It

A business needs an EIN if it does any of the following, per the Instructions for Form SS-4:

• Has any employees and files Form 941, 943, 944 or 945
• Operates as a corporation, S corporation or partnership
• Has a Keogh (HR-10) plan
• Files returns for excise taxes
• Withholds tax on income (other than wages) paid to a non-resident alien
• Is involved as the administrator of a trust, estate, real estate mortgage investment conduit, nonprofit, farmers’ cooperative or plan administrator

In practice, almost every US business that hires anyone (employee or contractor) ends up with an EIN. A single-member LLC owned by an individual can sometimes use the owner’s SSN, but most US payers ask for an EIN on Form W-9, and most banks require an EIN to open a business account.

Filing Deadlines

EIN applications themselves have no filing deadline, but the timing rules matter:

• Apply before you need it. The IRS recommends applying as soon as the entity is formed (and after state entity formation for LLCs and corporations). The online tool issues an EIN immediately for US-principal-place-of-business applicants.
• Form SS-4. Apply by fax (typically four-business-day turnaround), by mail (four to five weeks), or by phone for international applicants. See the Instructions for Form SS-4 for current contact details and the international EIN line.
• Responsible-party changes. The entity must report a change of responsible party within 60 days on Form 8822-B. The IRS uses the responsible-party record to authenticate callers and process correspondence.
• First filing after issuance. Once an EIN is issued, the entity should use it on the very next federal filing, even if its tax accounts are not yet fully open. Filings under SSN after the EIN issue date create reconciliation problems at the IRS.
• One online EIN per responsible party per day. The IRS limits the online tool to one EIN per responsible party per business day to prevent abuse.

Common Mistakes

• Paying a third party to get a free number. The EIN is free directly from the IRS. The IRS Apply for an EIN online page warns against fee-charging websites.
• Applying before forming the entity. For LLCs and corporations, state entity formation should come first. An EIN tied to a not-yet-formed entity can be invalid and may require correction with the IRS.
• Reusing an EIN after a structural change. A merger, conversion or change in legal form can trigger a “new EIN required” outcome under the IRS rules. Continuing to use the old EIN can invalidate returns.
• Forgetting to update the responsible party. Form 8822-B is due within 60 days of a change. Stale responsible-party records can cause the IRS to mail correspondence to the wrong person and refuse to authenticate phone calls.
• Using SSN on W-9 when an EIN exists. A US LLC with an EIN should use that EIN on Form W-9, not the owner’s SSN. Payers may issue 1099s under the SSN if the W-9 was wrong.

Related Forms

• TIN (Taxpayer Identification Number): the umbrella term that includes EIN, SSN, ITIN, ATIN and PTIN.
• Form W-9: where a US entity provides its EIN to a US payer.
• Form W-8BEN-E: where a foreign entity provides its US EIN to claim treaty benefits on US-source income.
• Form 1099-NEC: one of many information returns on which the payer’s EIN appears.
• ITIN: the equivalent IRS-issued TIN for individuals who do not qualify for an SSN.

Omnivoo Contract Management stores each vendor’s EIN against their certified W-9, runs IRS TIN matching to catch typos before the first payment, and reuses the verified EIN on every downstream 1099 filing.