TIN vs EIN
TIN is the umbrella term for every kind of IRS Taxpayer Identification Number. EIN is one specific subtype — the one issued to businesses. Here's the full picture, plus which one your LLC actually needs.
| TIN | EIN | |
|---|---|---|
| What it is | Umbrella category — any IRS Taxpayer Identification Number | One specific type of TIN, for businesses and entities |
| Includes | SSN, ITIN, EIN, ATIN, PTIN | Just the 9-digit business ID |
| Format | Varies (XXX-XX-XXXX for SSN/ITIN; XX-XXXXXXX for EIN) | XX-XXXXXXX (9 digits) |
| Issued by | IRS or SSA depending on subtype | IRS only |
| Used for | Identifying any US taxpayer | Identifying a business entity for federal tax, payroll, banking |
| Required for an LLC | Yes — the EIN is the LLC's TIN | Yes — multi-member always, single-member when banking/hiring |
| Cost | Varies (SSN free, ITIN free with W-7, EIN free) | Free from the IRS |
The five types of TIN
- SSN — Social Security Number. Issued by the SSA. The TIN for US citizens and permanent residents.
- ITIN — Individual Taxpayer Identification Number. For individuals who need to file a US tax return but can't get an SSN. Applied for via Form W-7.
- EIN — Employer Identification Number. For businesses and entities. Applied for via Form SS-4.
- ATIN — Adoption Taxpayer Identification Number. Temporary, for adopted children pending an SSN.
- PTIN — Preparer Tax Identification Number. For paid tax preparers signing returns.
When someone asks for your "Tax ID", they almost always mean either your SSN (if you're an individual) or your EIN (if you're a business). Forms like the W-9 explicitly say "Taxpayer Identification Number (TIN)" and let you write in either.
When forms say "TIN" — what do you actually write?
The most common context is IRS Form W-9, which contractors and vendors complete for clients. The W-9 has one field labeled "Taxpayer Identification Number (TIN)" with two checkboxes: SSN or EIN. The right answer depends on who's signing:
- Single-member LLC (disregarded entity), no employees: Write the owner's SSN or the LLC's EIN. The IRS prefers SSN per W-9 instructions, but most owners use the EIN to keep their SSN off vendor records. Either is technically valid.
- Single-member LLC taxed as S-corp or C-corp: Write the LLC's EIN. The election makes the LLC a separate taxpayer.
- Multi-member LLC: Write the LLC's EIN. Always.
- Sole proprietor with no LLC and no employees: Write your SSN (or your EIN if you have one — getting one is free and reduces SSN exposure).
SSN vs ITIN vs EIN — picking the right one
The three TIN subtypes that come up most often, side by side:
- SSN — Issued by the Social Security Administration to US citizens and authorized residents. Used for personal taxes, employment, banking, credit. Format: XXX-XX-XXXX.
- ITIN — Issued by the IRS to individuals who need to file US taxes but can't get an SSN (typically non-resident foreigners with US-source income, or non-resident spouses). Applied for via Form W-7. Format looks like an SSN but starts with 9. Does not grant work authorization or Social Security benefits.
- EIN — Issued by the IRS to businesses, partnerships, trusts, estates, and other entities. Format: XX-XXXXXXX. Free, permanent, never expires.
You can hold all three at once — your personal SSN, an EIN for your LLC, and (rarely) an ITIN for a different filing situation. They don't overlap or replace each other.
When an LLC actually needs an EIN (not just an SSN)
The IRS lists six triggers that require an EIN for an LLC:
- You have one or more employees.
- You file employment, excise, or alcohol/tobacco/firearms tax returns.
- You have a Keogh or other retirement plan.
- You're a multi-member LLC (taxed as a partnership).
- You've elected to be taxed as a corporation (C-corp or S-corp).
- You have a non-US owner.
Practically, even single-member LLCs without any of these triggers should get an EIN — because every US business bank account application requires one, and because using your SSN on vendor W-9s is an avoidable identity-theft exposure.
Looking up a forgotten TIN
- SSN: On your Social Security card, prior tax returns, W-2s. SSA can reissue your card; they will not tell you the number over the phone.
- EIN: On your CP-575 confirmation letter (the IRS sent it when issued), prior business tax returns, bank account opening packets. Lost both? Call the IRS Business & Specialty line at +1 (800) 829-4933 — they'll release it to an authorized owner over the phone, or issue a 147c letter by fax.
- ITIN: On the assignment letter the IRS sent. Lost? Call the IRS or submit Form W-7 (Renewal).
- Putting your SSN on vendor W-9s
A single-member LLC can technically use the owner's SSN, but every W-9 you send out then exposes it. Get a free EIN and use that on W-9s instead.
- Confusing EIN and ITIN
EIN is for the business; ITIN is for a person without an SSN. A non-US founder forming an LLC needs an EIN for the LLC — they only need an ITIN if they personally have a US tax-filing obligation.
- Paying a third party for an EIN you can get free
The IRS issues EINs for free at irs.gov (online for SSN holders, by fax/mail for non-US founders). Paid services are useful when you need someone to handle the fax process — not because the EIN itself costs anything.
- Reusing an old EIN after restructuring
Some changes (sole-prop → LLC, partnership → corp, new ownership of a sole-prop) require a brand-new EIN. The IRS publishes a list of triggers. Check before reusing.