The short answer: A federal tax ID, or EIN (Employer Identification Number), is a nine-digit number the IRS assigns to identify a business on its federal tax filings, written in the format 12-3456789. Corporations, partnerships, and any business with employees must have one, and most LLCs get one anyway because banks require it to open a business account. Applying directly with the IRS is free, and the online application issues the EIN immediately. The number never expires and is never reassigned, but a change of business structure generally requires a new one.
A CPA-led guide for founders and finance teams.
The plain answer first, then the detail your bookkeeper, attorney, or CPA will want, including the handful of mistakes that quietly cost businesses time and money.
An Employer Identification Number is the single piece of identification almost every U.S. business needs before it can do anything official: open a bank account, run payroll, file a return, or sign with a vendor. Yet it is one of the most misunderstood items on a founder’s setup checklist. This guide explains what the EIN actually is, who is required to have one, how to apply for it for free, and the handful of mistakes that quietly cost businesses time and money.
We have written this the way we would walk a client through it across a desk: the plain answer first, then the detail your bookkeeper, attorney, or CPA will want. Where a number on a later filing depends on it, we have flagged that too.
Key takeaways
- What is an EIN: a federal tax ID the IRS issues to identify a business, the business equivalent of a Social Security Number.
- Who must have one: any business with employees, all corporations and partnerships, and businesses filing employment, excise or certain other returns.
- Single-member LLC exception: with no employees, the owner can use their SSN, but most still get an EIN because banks require one.
- Free and fast: applying directly with the IRS costs nothing; online gives the number on the spot, fax takes about four business days, mail about four weeks.
- No SSN or ITIN: foreign owners can still get an EIN by fax, mail, or phone, just not through the online tool.
- One per day: the IRS issues only one EIN per responsible party per day, across all methods.
Keep it current: report responsible-party changes on Form 8822-B within 60 days, and get a new EIN if the business changes structure.
What a federal tax ID (EIN) actually is
A Federal Employer Identification Number (EIN) is a nine-digit number the IRS assigns to a business so it can be identified on tax filings, written in the format 12-3456789. People also call it a Federal Tax ID, a FEIN, or simply a business tax ID. The simplest way to picture it: the EIN is to your business what a Social Security Number is to a person.
The number does three quiet but important jobs. It identifies your entity to the IRS on every federal filing you make. It lets banks and vendors confirm who they are dealing with. And it keeps your business identity separate from your personal one, so you are not handing out your SSN every time a supplier needs a tax ID for invoicing.
An EIN is free, it does not expire, and once issued to a business it is never reassigned to anyone else, even if that business later closes.
EIN vs. SSN vs. ITIN: how they differ
Three nine-digit numbers do related jobs, and mixing them up is one of the most common early errors. Here is the clean distinction:
| Number | What it identifies | Who it belongs to |
|---|---|---|
| EIN | A business or other entity, for federal tax filing and reporting | The company itself |
| SSN | An individual, for personal income tax and benefits | A U.S. citizen or authorized resident |
| ITIN | An individual who must file U.S. tax but cannot get an SSN | A non-resident or foreign owner |
One practical note for the IRS application: the person applying for the EIN must supply their own SSN or ITIN as the identifier. A foreign founder without either can still obtain an EIN, but the route is by fax, mail, or phone rather than the online tool. We will come back to that under “How to apply.”
Example: Maya forms a single-member LLC for her design studio. She uses her SSN on the application and lists herself as the responsible party. The IRS issues the LLC its own EIN: 84-1234567. From that point on, when a client asks her studio for a W-9, she writes the EIN, not her SSN. Her personal number stays private, and the business is identified in its own right.
Who needs an EIN
Most businesses need one, and many that think they are exempt actually are not. You are required to obtain an EIN if any of the following is true:
- You have employees. Any business that pays wages needs an EIN to report payroll taxes. This includes a sole proprietor the moment they make a first hire.
- You operate as a corporation or partnership. C corporations, S corporations, and multi-member partnerships all need an EIN regardless of whether they have employees.
- You file certain tax returns. Returns for employment, excise, or certain other taxes require an EIN.
- You withhold tax on income paid to a non-resident. Withholding agents need an EIN to report it.
Beyond the strict requirement, most LLCs and corporations get one as a practical necessity because a bank will not open a business account without it. A single-member LLC with no employees is the one common case where the IRS does not strictly require an EIN (the owner can use their SSN), but even then, getting one is usually the right call to keep personal and business identity separate and to satisfy the bank.
Example: David runs a sole proprietorship as a freelance consultant and has used his SSN on tax filings for two years. In year three he hires his first part-time assistant. That single hire flips him into EIN territory: he now needs one to deposit and report payroll taxes. The business did not change its legal form; adding an employee alone created the requirement.
What you can do once you have one
An EIN is rarely the goal in itself; it is the key that unlocks the next several steps of running a business. With it in hand you can:
- Open a business bank account, since almost every bank requires it.
- Hire employees and set up payroll tax accounts.
- File federal and state business tax returns.
- Apply for business licenses and permits that ask for a tax ID.
- Build business credit and apply for loans in the company’s name.
- Provide a tax ID to vendors and clients on a W-9 without exposing your SSN.
Because so much downstream activity waits on the EIN, it is worth getting early. Founders routinely find their bank onboarding, payroll setup, and first vendor contracts all stalled on this one nine-digit number.
How to apply for an EIN, step by step
The application itself is short, and applying directly with the IRS is free. The form behind it is IRS Form SS-4; the online tool walks you through the same questions interactively. Before you start, gather a few things:
- The legal name and structure of the entity (sole proprietorship, partnership, LLC, corporation).
- The name and SSN or ITIN of the responsible party: the individual who ultimately owns or controls the business.
- A physical U.S. mailing address (the online tool will not accept a P.O. box as the primary address).
- The reason you are applying, for example, started a new business, hired employees, or changed entity structure.
The four routes to the IRS
| Method | Who it suits | Typical timing |
|---|---|---|
| Online | Applicants with a U.S. SSN or ITIN; the IRS-recommended route | EIN issued immediately on completion |
| Fax | Those who prefer paper or have no SSN/ITIN | Generally about four business days |
| Those not in a hurry | Around four weeks | |
| Phone | International applicants whose principal business is outside the U.S. | Issued during the call if approved |
Two guardrails are worth knowing in advance. The online application is available during IRS service hours, Monday through Friday. And the IRS issues only one EIN per responsible party per day, across all methods, so if you are setting up several entities, plan to space the applications out.
Example: A founding team incorporates a Delaware C corporation on a Monday and needs the EIN before a Thursday bank appointment. The CEO, who is the responsible party, applies online with her SSN during IRS service hours and receives the EIN on the spot. Because the corporation already exists on paper, the bank appointment goes ahead as planned. Had she instead needed to mail Form SS-4, the four-week turnaround would have pushed everything back.
Keeping the EIN current
The EIN itself never changes, but the information attached to it can. If your responsible party changes, or your business address or location changes, the IRS expects you to report it on Form 8822-B, and changes to the responsible party must be reported within 60 days. Keeping this current matters because IRS notices go to the address and contact on file; a stale record means missed correspondence.
One more point that surprises people: a change of business structure generally requires a brand-new EIN, not an update to the old one. If you convert a sole proprietorship or general partnership into an LLC or corporation, you usually cannot carry the old EIN forward. You apply for a new one for the new entity.
Example: A two-person partnership has operated under one EIN for years. They decide to incorporate as an S corporation for tax reasons. Even though the same two people run the same business, the new corporation is a different legal entity, so it needs its own new EIN. The old partnership EIN is retired rather than reused.
Common mistakes to avoid
1. Naming a nominee instead of the real responsible party
The IRS wants the individual who actually controls the entity, not a stand-in. A nominee on the application creates privacy and accuracy problems later.
2. Reusing an old EIN after changing structure
Converting a sole proprietorship or partnership into an LLC or corporation generally requires a new EIN, not the old one.
3. Forgetting the one-per-day limit
If you are forming several entities, you can only obtain one EIN per responsible party per day, a surprise that can derail a tight setup timeline.
4. Letting the responsible party record go stale
Failing to file Form 8822-B after a change means IRS notices go to the wrong place, and the 60-day clock is easy to miss.
Setting up a new business? Get the foundations right.
A sole proprietorship is a great place to start, but the moment you take on partners, seek funding, or convert to an LLC or corporation, the tax and compliance questions get more involved. Countsure is a CPA-led firm that helps founders choose the right structure, set up clean books and tax filings, and stay compliant as the business grows.
Frequently Asked Questions
1. Is an EIN the same as a federal tax ID number?
Yes, in common usage. An EIN (Employer Identification Number) is one type of federal tax ID number issued by the IRS to identify a business. People also call it a FEIN or federal EIN. It must appear on the business’s federal tax filings.
2. Does my LLC or corporation actually need one?
Corporations and multi-member LLCs generally must have an EIN whether or not they employ anyone. A single-member LLC with no employees is the main exception, since its owner can use their SSN, but most still get an EIN because banks require it to open a business account.
3. How much does an EIN cost?
Nothing, if you apply directly with the IRS. The number is free. Some founders pay a service to handle the paperwork, but that fee is for the convenience, not for the EIN itself.
4. Can I get an EIN without a Social Security Number?
Yes. A foreign owner without an SSN or ITIN cannot use the online tool, but can still obtain an EIN by submitting Form SS-4 by fax or mail, or by applying by phone if the principal business is outside the U.S.
5. I'm converting my sole proprietorship to an LLC. Can I keep my EIN?
Generally no. A change of business structure usually requires a new EIN for the new entity. The old number is retired rather than carried forward.
6. What do I do if my responsible party or address changes?
File Form 8822-B with the IRS. Changes to the responsible party must be reported within 60 days so that IRS notices continue reaching the right person.
Related Countsure Blogs
- What Is a DBA? When and How to File a “Doing Business As” Name Explains how to trade under a name other than your legal one, and why a DBA gives no liability protection or tax change.
- Single-Member LLC vs. Sole Proprietorship: Which Structure Fits Your Business? Compares the two most common one-owner structures on liability, taxes and upkeep.
- What Is an S Corporation? How an S Corp Works Explains the S corp as a federal tax election, who qualifies, and how it compares to an LLC and a C corp.
Parth Shah, Managing Director
(CPA-US, FCA, RV-S&FA, DISA)
Parth Shah who is head of Accounts and Book keeping has experience of more than 10 years. A Certified Public Accountant – US, fellow Chartered Accountant, Registered Valuer and Diploma in Information System Audit.
