An entity ID is a unique number a government agency assigns to identify your business for tax, regulatory, or contracting purposes. Most businesses deal with at least two: a federal Employer Identification Number (EIN) from the IRS, and one or more state-issued numbers tied to formation and tax collection. Businesses that want to work with the federal government also need a Unique Entity ID from SAM.gov. Which entity IDs you actually need depends on how your business is structured, where it operates, and what it plans to do.
The Federal EIN
The EIN is a nine-digit number the IRS issues to businesses, tax-exempt organizations, trusts, estates, and other entities for federal tax purposes.1Internal Revenue Service. Employer Identification Number It functions like a Social Security number for the business, keeping the entity’s tax obligations separate from the owner’s personal finances. Using an EIN instead of your SSN on business paperwork also reduces your personal exposure to identity theft.
You need an EIN if your business is a corporation, a partnership, or a multi-member LLC, even with zero employees. You also need one if the business hires workers, pays excise taxes, or administers a trust, estate, or retirement plan.2Internal Revenue Service. Get an Employer Identification Number
The Single-Member LLC Wrinkle
Single-member LLCs sit in a gray zone. By default, the IRS treats them as disregarded entities, which means you can use your own Social Security number for income tax purposes and technically don’t need an EIN, provided you have no employees and no excise tax obligations. Most single-member LLCs get one anyway. Banks often require an EIN to open a business account, and some state tax authorities want a federal EIN on file.3Internal Revenue Service. Single Member Limited Liability Companies
Once a single-member LLC hires an employee, an EIN is mandatory. The LLC must use its own name and EIN for all employment tax reporting and payment, even though income tax still passes through to the owner personally.3Internal Revenue Service. Single Member Limited Liability Companies
How to Get an EIN
The IRS charges nothing for an EIN. Worth repeating, because plenty of third-party sites will charge you $79 to $300 to file the same free application. If a site is asking for payment, you’re not on the IRS site.2Internal Revenue Service. Get an Employer Identification Number
Before you start, have your entity’s legal name, principal business address, entity type, and the reason for applying ready. You’ll also need the full name and taxpayer identification number of the “responsible party,” which the IRS defines as the individual who ultimately owns or controls the entity or effectively controls its funds. For most small businesses, that’s the owner. The responsible party must supply a Social Security number or Individual Taxpayer Identification Number (ITIN). Government entities may use an EIN instead.4Internal Revenue Service. Instructions for Form SS-4
The fastest path is the IRS online EIN assistant, which walks you through the questions and issues your number immediately on approval. The tool is available Monday through Friday from 6:00 a.m. to 1:00 a.m. Eastern, Saturday from 6:00 a.m. to 9:00 p.m. Eastern, and Sunday from 6:00 p.m. to midnight Eastern.2Internal Revenue Service. Get an Employer Identification Number The whole process runs under ten minutes if your information is on hand.
If the online tool isn’t an option, you can submit the paper Form SS-4 by fax or mail. Fax applications generally return an EIN within four business days. Mail is the slowest route, typically four to five weeks.4Internal Revenue Service. Instructions for Form SS-4
Applying From Outside the US
The online tool requires a U.S. address. If your business is based abroad and the responsible party has no Social Security number or ITIN, you can still apply by fax or mail using Form SS-4. Enter “foreign” or “N/A” on line 7b where the form asks for the responsible party’s taxpayer ID number.4Internal Revenue Service. Instructions for Form SS-4 Processing times are the same: about four business days by fax, four to five weeks by mail.
When You Need a New EIN
Your EIN stays with the business through name changes, address changes, and even changes in ownership percentage. Certain structural changes end the old entity and create a new one in the IRS’s eyes, and those do require a fresh number. The triggers vary by business type.5Internal Revenue Service. Publication 5845 – Do You Need a New Employer Identification Number
- Sole proprietors need a new EIN when incorporating, taking on partners to form a partnership, buying or inheriting an existing business, or entering bankruptcy.
- Corporations need a new EIN when receiving a new charter from the secretary of state, becoming a subsidiary, converting to a partnership or sole proprietorship, or creating a new corporation through a statutory merger.
- Partnerships need a new EIN when incorporating, dissolving so one partner continues as a sole proprietor, or ending the old partnership and starting a new one.
- Estates and trusts need a new EIN when an estate creates a separate trust with estate funds, when a trust converts to an estate, or when a living trust terminates by distributing property to a residual trust.
The common mistake is assuming any change requires a new number. Changing your business name, adding a location, or changing filing status does not. Only the structural changes above do.5Internal Revenue Service. Publication 5845 – Do You Need a New Employer Identification Number
State-Level Business IDs
A federal EIN is one piece. Most businesses also need one or more numbers from their state.
State Entity or Registration Number
When you register a corporation or LLC with your state’s secretary of state or equivalent office, the state assigns an entity number tied to your formation documents. You’ll reference it when filing annual reports, amending your articles, or requesting certificates of good standing. The number is issued automatically during formation, so there’s no separate application. Filing fees vary widely, generally $50 to $500.
State Tax ID
If your business collects sales tax, has employees in a state, or owes franchise tax, you’ll need a separate state tax ID from that state’s department of revenue or tax authority. The application process varies. Some states issue the number online within a day; others take weeks by mail.
Online sellers should watch for economic nexus. After the Supreme Court’s 2018 decision in South Dakota v. Wayfair, states can require out-of-state sellers to collect sales tax once they cross a sales threshold in that state, even without any physical presence. The most common threshold is $100,000 in annual sales, though a handful of states set it at $250,000 or $500,000, and some also count individual transactions. Selling across state lines can mean tax IDs in several states.
The Unique Entity ID for Federal Contracting
If your business wants to bid on federal contracts or apply for federal grants, you need a Unique Entity ID (UEI), a 12-character alphanumeric identifier assigned through SAM.gov, the federal System for Award Management. The UEI replaced the DUNS number for all federal procurement on April 4, 2022, and the option to enter a DUNS number has been removed from SAM.gov entirely.6U.S. General Services Administration. Unique Entity Identifier Update
A UEI is free. You can complete a full entity registration on SAM.gov, which is required to bid on contracts or apply for grants directly, or request a UEI only, which is enough if you’re just a sub-awardee. Full registration asks for detailed business information and can take up to 10 business days to activate. You then have to renew every 365 days to stay current.7SAM.gov. Entity Registration A UEI-only request needs just your legal business name and physical address.
Other Identifiers Worth Knowing
DUNS Number
The Data Universal Numbering System (DUNS) number is a nine-digit identifier from Dun & Bradstreet linked to your business credit profile. It’s no longer used for federal contracting, but lenders, suppliers, and potential partners may still check your Dun & Bradstreet file when evaluating creditworthiness. If building business credit matters to you, it’s still worth having.
Local Registration Numbers
Some cities and counties issue their own business registration or license numbers, typically required before you can operate within the municipality and tied to local business taxes and zoning. Requirements vary enormously, so check with your city or county clerk’s office.
Beneficial Ownership Reporting
The Corporate Transparency Act originally required most small businesses formed in the United States to report their beneficial owners to the Financial Crimes Enforcement Network (FinCEN), with an optional “FinCEN identifier” available to streamline the process. In March 2025, FinCEN published an interim final rule exempting all domestically formed companies and their U.S. beneficial owners from this reporting requirement.8Financial Crimes Enforcement Network. Beneficial Ownership Information Reporting The rule now applies only to entities formed under foreign law that have registered to do business in a U.S. state or tribal jurisdiction. If your business was formed in any U.S. state, you don’t currently need to file a beneficial ownership report or get a FinCEN identifier.