Taxpayer Identification Number: Types and Who Uses Each

Q: What is a taxpayer identification number?

A taxpayer identification number is a category, not one specific number: it is the collective name for the five identifiers the IRS relies on when it administers tax law. The group covers the Social Security number, the employer identification number, the individual taxpayer identification number, the adoption taxpayer identification number, and the preparer tax identification number. The Social Security Administration hands out the first of these and the IRS hands out the remaining four, and all but one of them run to nine digits. So a form that asks for a taxpayer identification number is really asking which member of the group fits the person or business signing it. That is why an individual and a company fill in the same box with different numbers.

Q: Is a taxpayer identification number the same as an EIN?

No. The employer identification number is just one of the five identifiers the phrase taxpayer identification number covers, so the two terms are not interchangeable. On a payee form the difference is practical: a business entity is expected to supply its employer identification number, while an individual is expected to supply a Social Security number. Treating the terms as synonyms is the single most common way a name ends up paired with the wrong number, and nothing flags the error on the day it happens. You find out months later, once the IRS has compared your filing with its own records and written to you about the returns that did not match.

Q: What are the five types of taxpayer identification numbers?

The five are the Social Security number issued by the Social Security Administration on Form SS-5, the employer identification number issued by the IRS on Form SS-4, the individual taxpayer identification number issued by the IRS on Form W-7, the adoption taxpayer identification number issued by the IRS on Form W-7A, and the preparer tax identification number, which the IRS issues through an online sign-up or on paper Form W-12. A small employer realistically encounters three of them: the Social Security number of an employee or of a contractor who never formed an entity, the employer identification number of an incorporated vendor, and the individual taxpayer identification number that a new hire or a contractor may offer in place of a Social Security number. Adoption and preparer numbers exist outside the payroll relationship entirely.

Q: Which taxpayer identification number do I collect from a contractor?

You collect the number the contractor certifies on Form W-9, and the contractor’s legal structure decides which one that is, not your preference. A sole proprietor provides a Social Security number, or an employer identification number if they obtained one. A partnership or a corporation provides the employer identification number it holds as an entity. A single-member limited liability company that is disregarded for tax purposes uses its owner’s number rather than one of its own. Picking among these is not your job. Your job is to get the signed form before the first payment, file it with the payee record, and confirm the name and number pair against IRS records before any filing carries it.

Q: Can an employee work using an ITIN?

No. The individual taxpayer identification number is a federal tax-filing identifier and nothing more: holding one gives no right to work in the United States and no claim to Social Security benefits. IRS guidance tells employers directly not to take one instead of a Social Security number, either to identify an employee or as a basis for employment. Whether someone may legally work is a separate question, answered through Form I-9 and the documents that process accepts, never through a tax number. A holder who later gains work authorization applies to the Social Security Administration for a Social Security number, and from then on their wages are reported under it.

Q: How do I check that a name and taxpayer identification number match?

Use one of two free federal services, chosen by who is on the other side of the payment. Payers of reportable payments check contractors and other payees through the IRS on-line matching program, which answers straight away for as many as 25 pairs entered by hand and within 24 hours for a bulk file of up to 100,000. Employee names and numbers go to the Social Security Administration instead: 10 at a time with an instant answer, or up to 250,000 in an uploaded file. That second service exists only to get wage reports right. It is not a pre-employment screening tool, and nothing it returns should drive an adverse decision about a worker.

Q: What happens if a 1099 has a missing or wrong taxpayer identification number?

It is treated as an incorrect information return, and the penalty depends on how quickly you fix it. Under Revenue Procedure 2025-32, a return required to be filed in 2027 costs $60 if you correct it within 30 days, $130 if you correct it by August 1, and $340 if the correction comes later or never. Intentional disregard is priced separately at $690 per return or 10 percent of the amounts that should have been reported, whichever is greater. A mismatch also triggers a CP2100 or CP2100A notice, which starts a sequence of payee notices and can require backup withholding at 24 percent on future payments to that payee until a correct certification arrives.

Q: How do I find my business taxpayer identification number if I have lost it?

Four places usually have it on file, so check them before you call anyone: the confirmation notice the IRS sent when it assigned the number, the bank where the business account is held, any state or local agency you applied to for a license, and any business tax return you have already filed. If all four come up empty, call the IRS Business and Specialty Tax Line at 800-829-4933, Monday to Friday, 7 a.m. to 7 p.m. local time, and it will look up the number for an authorized person. When a bank or a payer wants written proof instead of your word, ask for Letter 147C. An employee’s Social Security number works differently, because no employer lookup exists for it at all. It comes from the employee and their card, and any correction has to come from the Social Security Administration.

A taxpayer identification number is any of five IRS identifiers. Which one you collect from employees and contractors, and how to check it before filing.

Nick Anisimov

FirstHR Founder

Payroll•

August 18, 2026

•

12 min

Taxpayer Identification Number

The phrase on every payee form is a category rather than a number, and five different identifiers sit inside it: which one you collect from an employee, which one you collect from a contractor, what to do when a new hire hands you one that cannot be used for wages, and how to check the pair before it reaches a filing

The first contractor I ever paid sent back a form with a Social Security number written in the box. The box was labeled taxpayer identification number, and I spent an evening convinced I had asked for the wrong thing and would have to ask again.

I had not. That evening was the cost of not knowing something small: taxpayer identification number is not a number at all. It is a category, five identifiers belong to it, and every payee form asks for the category while quietly expecting one specific member of it.

What follows is the employer’s view of that family: which member you collect from whom, what to do when somebody hands you one that cannot be used for wages, how to check a name and number pair before it reaches a filing, and what the errors cost.

I build the people and records tooling for companies without an HR department at FirstHR, which is an onboarding and HR platform rather than a payroll provider. This is general information, not tax advice.

TL;DR

A taxpayer identification number is the umbrella term for five federal identifiers: the Social Security number, the employer identification number, the individual taxpayer identification number, the adoption number, and the preparer number. Employers collect a Social Security number from employees and either that or an employer identification number from contractors. An uncorrected wrong pair costs $340 per return.

What the Phrase Actually Means

A taxpayer identification number is an identifying number used in administering federal tax law, and it is a category rather than one number. Five identifiers sit inside it, four of them nine digits long, issued by either the IRS or the Social Security Administration (Internal Revenue Service).

Definition

Taxpayer identification number (TIN)

The umbrella term for the numbers the IRS uses to identify a taxpayer on a return, a payment, or an information return. It covers the Social Security number, the employer identification number, the individual taxpayer identification number, the adoption taxpayer identification number, and the preparer tax identification number. It is not a number you can apply for, because there is no application for the category itself, only for its members.

This is why the phrase feels slippery in practice. A bank, a payment platform, and a payee form all use it, and each of them means a different specific number depending on who is answering. The category is the question. The member is the answer.

Internal employee numbers are a separate matter with no tax meaning at all. The identifiers a business assigns for its own records are an administrative convenience, and they never go in a box asking for a taxpayer identification number.

The Five Types and Who Issues Them

Four of the five are issued by the IRS and one by the Social Security Administration, each through its own application. Knowing which agency owns which number tells you where a replacement or a correction has to come from, which is the part that matters when something is wrong.

SSN, Social Security number

Issued by: Social Security Administration, on Form SS-5Belongs to: An individualThe number an employee gives you and the number that goes on their W-2. A sole proprietor without a business number also uses it on a W-9.

EIN, employer identification number

Issued by: IRS, on Form SS-4Belongs to: A business, estate, trust, or other entityThe number your own business files payroll returns under, and the number an incorporated contractor gives you instead of a personal one.

ITIN, individual taxpayer identification number

Issued by: IRS, on Form W-7Belongs to: An individual who must file but cannot get a Social Security numberNine digits beginning with a 9. It exists for federal tax reporting and nothing else. It does not authorize work and cannot be used for wage reporting.

ATIN, adoption taxpayer identification number

Issued by: IRS, on Form W-7ABelongs to: A child in a pending domestic adoptionTemporary, and issued so adoptive parents can claim the child while the Social Security number is still pending. An employer will never collect one.

PTIN, preparer tax identification number

Issued by: IRS, online or on paper Form W-12Belongs to: A paid tax return preparerIt identifies the person who prepared a return for compensation. It appears on your filings if you use an accountant, and never on a payee form.

Only three of the five ever reach a small employer: the Social Security number of an employee or of a contractor who never incorporated, the business number of an entity you pay, and the individual number a new hire or a contractor may hand you in place of a Social Security number.

The one people underestimate is the individual number. It looks like a Social Security number, it is formatted like one, and it begins with a 9. It also cannot do the thing an employer most often needs a number to do, which is carry wages on a W-2.

What Each Number Looks Like

Punctuation is what tells these numbers apart on sight, and it is the fastest check available when a form comes back. An employer identification number is written as two digits, a hyphen, then seven more, for example 12-3456789, which is the format the IRS uses in its own instructions to Form SS-4.

A Social Security number is nine digits in three groups of three, two, and four. Under the Social Security Administration randomization rules, the agency never assigns one whose first three digits are 000, 666, or 900 through 999. That last exclusion keeps individual taxpayer identification numbers, all of which begin with a 9, from colliding with Social Security numbers.

An individual number is nine digits beginning with 9 and formatted exactly like a Social Security number, which the IRS writes as NNN-NN-NNNN.

Knowing the shapes has one small, real use: a number arriving in a two-and-seven grouping is a business number, so a personal name beside it is a mismatch to resolve before filing, unless the payee is a sole proprietor who obtained one.

Which Number You Collect From Whom

The number you collect depends on how the other party is organized, not on which relationship you are in. An employee always gives a Social Security number. A payee gives whichever identifier matches the entity that legally earned the money, as the Form W-9 instructions spell out for each type of payee.

Who you are paying	Number they give you	Where you collect it
An employee	Social Security number	Form W-4 at hire, with the name exactly as it appears on the Social Security card
A sole proprietor contractor	Their Social Security number, or an employer identification number if they have one	Form W-9, before the first payment
A single-member LLC that is disregarded	The owner’s number rather than the company’s	Form W-9, where line 1 carries the owner’s legal name
A partnership or a corporation	The entity’s employer identification number	Form W-9, signed by somebody authorized for the entity
An LLC that elected corporate treatment	The company’s employer identification number	Form W-9, with the tax classification box completed
A foreign person or foreign entity	Not a domestic number at all	The W-8 series rather than a W-9

The collection form is doing more than gathering digits. Form W-9 is a signed certification of the name and number pair, and the signature is what makes it a defense when the pair later turns out to be wrong.

Getting the answer right also depends on getting the relationship right first. If somebody who should be an employee is being paid as a contractor, no amount of correct paperwork fixes it, and worker misclassification carries consequences that dwarf a reporting penalty.

Foreign Tax Identification Number

A foreign tax identification number is the identifier a payee’s own country of tax residence issued to them, and it is what a foreign person puts on a Form W-8BEN in place of a US number. None of the domestic identifiers applies to them, which is why a W-9 is the wrong form to send.

The instructions to Form W-8BEN call it the foreign tax identifying number and put it on line 6a. The number is required there when the payee holds an account at a US office of a financial institution and receives US-source income reportable on Form 1042-S.

Two kinds of payee are excused from that requirement: a resident of a US territory, and a payee whose jurisdiction appears on the IRS list of places that do not issue one. Line 6b carries a checkbox for a payee who is not legally required to hold one.

Your part in this is narrow. Collect the right form before the first payment and keep it with the rest of the payee file. There is nothing to check a foreign number against, since the federal matching services hold US records only, and payments to a foreign person carry withholding rules of their own that are worth an accountant’s time.

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The Number Your Business Gives Out

When your business is the payee rather than the payer, the number you provide is your employer identification number if you are an entity, and your own Social Security number if you are a sole proprietor who never obtained one. Both are valid answers to the same question.

Plenty of sole proprietors get a business number anyway, for a reason that has nothing to do with tax law. It keeps a personal Social Security number off every form handed to a client. The employer identification number itself is free.

The number your business files under also appears on every W-2 you issue and every information return you file, which is why it belongs in your permanent payroll records rather than in somebody’s memory.

When a New Hire Presents an ITIN

You cannot use it for employment. IRS guidance to employers states the position without qualification: do not accept an individual taxpayer identification number in place of a Social Security number for employee identification or for work (Internal Revenue Service).

The reason sits in what the number is for. The IRS issues it for federal tax purposes only, to people who have a filing obligation but are not eligible for a Social Security number. It does not authorize legal work in the United States and it does not qualify anybody for Social Security benefits or the earned income credit.

A tax number is not work authorization

Employment eligibility is established through the I-9 process and the documents that process accepts, never through a tax identifier. Presenting an individual taxpayer identification number says nothing about whether somebody may legally work, and treating it as if it did creates exposure on both sides at once.

The practical route is to keep the two questions apart. Work authorization is settled by I-9 documentation, on its own timeline, using the list of acceptable documents. Wage reporting is settled by a Social Security number, which somebody who becomes work authorized obtains from the Social Security Administration.

These numbers also expire. According to the IRS, an individual number that goes unused on a federal return for three consecutive tax years expires on December 31 after that third year, and renewal runs on Form W-7 (Internal Revenue Service). The holder gets no reminder, so the discovery usually happens during a filing.

Expiry does not reach every use of the number. The IRS says an expired individual number may still go on an information return reporting payments the holder received, so a 1099 you file for a contractor is not blocked by it. What the expiry stops is the return the holder files themselves, which is their problem rather than yours.

What worked for me

I keep the tax number and the work authorization document on separate steps of the same onboarding flow, with different owners. When they sat on one screen, people filled one in from the other, and every correction after that was a conversation nobody wanted to have. Splitting them cost one extra click and removed the whole category of mistake.

Checking the Pair Before You File

Two free federal services exist for this, one for payees and one for employees, and neither is widely used by small employers. The IRS on-line matching program covers payees, taking up to 25 name and number combinations on screen with immediate results, or up to 100,000 in a single file with results inside 24 hours (Internal Revenue Service).

For employees, the Social Security Administration runs a verification service that checks names and numbers against its own records: 10 at a time on screen for immediate results, or up to 250,000 by file upload with results usually the next government business day.

The employee service exists only to make wage reporting accurate, and that limit is worth stating plainly: a result from it is not evidence about immigration status or a basis for an adverse decision about a worker. Using it that way creates legal exposure of its own. Kept to their intended purpose, both services fit into the same five-step routine.

Collect before the first payment

Ask for the signed certification form as part of setup, not as part of year-end. The request is routine before money moves and awkward afterward, and the response rate difference is not small.

Check the name against the source document

Match the legal name to the Social Security card for an employee and to the certification form for a payee. A trading name in the legal name field is the mismatch that survives every visual check.

Run the pair through the right service

Payees go through the IRS matching program, employees through the Social Security Administration service. Enrollment for the IRS program requires an account and payer status, so do it before the week you need it.

Resolve mismatches in writing

Go back to the person with a specific request: confirm the legal name and the number as they appear on the card or the IRS letter. Keep the reply. It becomes your record of a reasonable attempt.

Re-check before the annual filing run

Names change, entities restructure, and individual numbers expire. A second pass in the weeks before filing catches the drift that a single check at hire never could.

Those five steps only hold together if each one leaves a date behind. The sheet below is where that happens: one row per payee and one row per employee, with a column for the day the signed form arrived, the day the pair was checked, what came back, and the day it was checked again before the filing run. Fill it as you go rather than reconstructing it in January.

Name and Number Collection and Match Log

	A	B	C	D	E	F	G	H	I	J
1	Legal name on the certification form	Trade name, if different	How they are organized	Number type on file	Last four digits	Signed form received on	Pair checked on	Result	Action taken	Re-checked before filing on
2
3
4
5
6
7
8	Note	Record only the last four digits here. The full number belongs in the record system that holds the rest of the payee file, with access limited to the people who process payments.
9	Note	Open a row when the relationship starts, not when the filing season does.

When a pair does not match, the fourth step is the one people improvise, and improvising it is what leaves you with a phone call nobody can produce later. Send the request as a document instead, ask for the name and the number exactly as they appear on the source paperwork, and keep the signed reply in the same file as the certification form.

Name and Number Confirmation Request

CONFIRMATION OF LEGAL NAME AND TAXPAYER IDENTIFICATION NUMBER

To: [Payee or Employee Name]

From: [Company Name], [Your Name], [Title]

Date:

Re: [Contract, invoice, or payroll reference]

WHY YOU ARE RECEIVING THIS

We are confirming the name and taxpayer identification number we hold for you before we file anything that carries it. The pair on file did not match the records of the agency that issued the number, which is most often a difference in how the name was written rather than a wrong number.

[Include for contractor payees: If we do not receive a valid certification, federal rules may require us to begin backup withholding on future payments to you.]

[This letter is our own request, sent after we checked the pair ourselves. If the mismatch reached you because the IRS sent us a CP2100 or CP2100A notice, the payee notice required in that situation has its own prescribed wording and timing, and this letter does not replace it.]

WHAT WE CURRENTLY HAVE ON FILE

Name on file:

Type of number on file (Social Security number, employer identification number, other):

Last four digits on file:

Document this came from, and the date we received it:

WHAT WE NEED BACK FROM YOU

•The legal name exactly as it appears on your Social Security card, or on the IRS notice that assigned your employer identification number

•The type of number that belongs to that name

•A corrected and signed certification form if either the name or the number above is wrong

•A reply even if everything above is already correct, so the confirmation is on record

YOUR RESPONSE

Legal name as it appears on the source document:

Type of number:

Everything on file is already correct: [ ] Yes [ ] No

Corrected certification form attached: [ ] Yes [ ] No

Signature:

Printed name:

Date:

FOR INTERNAL USE

Request sent on:

Reply received on:

Corrected certification filed on:

Pair re-checked on:

Result of the re-check:

Filed in the payee or employee record by:

Building the check into your year-end payroll sequence is what makes it happen. As a standalone task that somebody remembers to do, it does not survive a busy quarter.

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What a Missing or Wrong Number Costs

A missing or incorrect number makes an information return incorrect, and the per-return penalty slides with how fast you fix it. For returns required to be filed in 2027, IRS Revenue Procedure 2025-32 sets it at $60 within 30 days, $130 by August 1, $340 after that, and $690 or more where the failure is intentional.

When it is corrected	Penalty per return	What this looks like in practice
Within 30 days of the due date	$60	You caught it yourself, filed a correction, and the cost is an annoyance
After 30 days, by August 1	$130	A mismatch notice arrived and you acted on it in the same season
After August 1, or never	$340	The return stayed wrong through the cycle, which is the common small business outcome
Intentional disregard	$690, or 10 percent of the amounts that should have been reported if greater	No maximum applies, and the amount is a floor rather than a ceiling

The number that should drive the process

$340 per return is the penalty for an information return with a missing or incorrect taxpayer identification number that is not corrected by August 1 of the filing year, for returns required to be filed in 2027. Thirty contractors with unchecked numbers is a five-figure exposure created by a step that takes an afternoon (IRS, Revenue Procedure 2025-32).

The penalty is not the whole cost. When a filing carries pairs that do not match IRS records, the IRS sends a CP2100 or CP2100A notice listing them, and that notice starts a clock.

Publication 1281 gives you 15 business days from the date of the notice, or the date you received it if that is later, to send the payee a B notice of your own, the prescribed warning that backup withholding may follow (IRS Publication 1281).

Backup withholding, where you hold back part of each payment for the IRS, starts if nothing comes back. The IRS requires it to begin no later than 30 business days after you received the notice, at 24 percent of every future payment to that payee (Internal Revenue Service). The whole sequence begins with a pair nobody checked.

The reporting threshold has changed the arithmetic. For payments made on or after January 1, 2026, nonemployee compensation is reportable at $2,000 under the One Big Beautiful Bill Act, up from $600 for payments before that date (IRS instructions for Forms 1099-MISC and 1099-NEC). Fewer small payees now generate a return, and the ones that do tend to be the relationships worth getting right.

The higher threshold did not merge the two contractor information returns, which are still filed separately and on separate schedules. Nonemployee compensation goes on its own form with a January 31 deadline, which is the earlier of the two.

Where Small Employers Get This Wrong

Almost every failure I have seen traces back to timing rather than to knowledge. The number is collected late, checked never, and stored somewhere that is not a system of record. The pattern repeats across companies that have nothing else in common.

Treating the category as a synonym for the business numberA form asking for a taxpayer identification number is asking which member of the family applies to the party signing it. An individual answering with a company’s business number, or a company answering with a personal one, produces a pair that will not match IRS records.

Accepting a name that does not match the numberThe check is on the pair, not the number alone. A contractor who trades under a brand name but registered the number under a personal legal name is the most common mismatch, and it passes every visual inspection you can do.

Collecting the number after the work is finishedOnce the invoice is paid, the leverage to ask is gone. The number is easy to get before the first payment and surprisingly hard to get in January, when the person has moved on and has no reason to reply.

Storing the number in an email threadA nine-digit identifier sitting in an inbox is a data problem waiting to happen. It belongs in the record system that holds the rest of the payee file, with access limited to the people who actually process payments.

Assuming a number that worked once still worksAn individual number that goes unused on a federal return for three consecutive years expires. A business that restructures may be issued a new number. Neither event sends you a notice, so both surface at filing time.

Three of these five are solved by one habit: collect the number before the first payment and check the pair the same week. The other two need a proper place to store it and a re-check before filing.

The fix is unglamorous. Make the number part of the intake step for both employees and payees, check the pair while the person is still responsive, and keep it with the rest of the file. Onboarding paperwork that collects it as a matter of course removes the annual scramble entirely.

It also helps to know which relationship you are actually in before the paperwork starts. The contractor relationship and the employment relationship collect the number on different forms, and sorting that out afterward is far more expensive than sorting it out first.

Key Takeaways

Taxpayer identification number is a category covering five federal identifiers, not a single number you can apply for.

Employees give a Social Security number; payees give whichever identifier matches the entity that earned the money, certified on a signed form.

An individual taxpayer identification number exists for federal tax reporting only and can never carry wages or establish work authorization.

Two free federal services check name and number pairs, one for payees through the IRS and one for employees through the Social Security Administration.

An uncorrected missing or wrong number costs $340 per return for filings required in 2027, and can trigger backup withholding at 24 percent.

Collect the number before the first payment and check the pair the same week, because both get harder once the relationship has ended.

Frequently Asked Questions

What is a taxpayer identification number?

It is the umbrella term for the identifying numbers the IRS uses to administer tax law, and it is a category rather than a single number. Five identifiers belong to it: the Social Security number, the employer identification number, the individual taxpayer identification number, the adoption taxpayer identification number, and the preparer tax identification number.

Is a taxpayer identification number the same as an EIN?

No. An employer identification number is one member of the category, not another name for it. An entity gives that number, an individual gives a Social Security number, and reading the two phrases as interchangeable is the most common cause of a pair that fails to match IRS records months after it was written down.

What are the five types of taxpayer identification numbers?

They are the Social Security number (Form SS-5), the employer identification number (Form SS-4), the individual taxpayer identification number (Form W-7), the adoption taxpayer identification number (Form W-7A), and the preparer tax identification number (online, or on paper Form W-12). A small employer meets three of the five in practice.

Which taxpayer identification number do I collect from a contractor?

Whichever one they certify, which depends on how they are organized. A sole proprietor gives a personal number or a business number if they have one; a partnership or corporation gives the entity number; a disregarded single-member company reports under its owner. Paying contractors correctly starts with getting that certification before the first payment.

Can an employee work using an ITIN?

No. It exists for federal tax reporting only, does not authorize employment in the United States, and confers no Social Security eligibility. IRS guidance tells employers not to accept one in place of a Social Security number for employee identification or for work, and employment eligibility is settled through the I-9 process instead.

How do I check that a name and taxpayer identification number match?

Through the free federal services. The IRS on-line matching program handles payees, taking 25 pairs on screen with immediate results or 100,000 by file within 24 hours. The Social Security Administration verifies employee names and numbers for wage reporting, 10 on screen or 250,000 by upload.

What happens if a 1099 has a missing or wrong taxpayer identification number?

It counts as an incorrect information return, priced by how quickly you fix it: $60 within 30 days, $130 by August 1, and $340 after that for returns required to be filed in 2027. A mismatch also produces a notice from the IRS that can lead to backup withholding, and the contractor filing process is where the correction gets made.

How do I find my business taxpayer identification number if I have lost it?

Start with the notice the IRS issued when the number was assigned, then work outward: the bank that holds the business account, any state or local licensing agency you applied to, and past business tax returns. If none of those turn it up, the IRS Business and Specialty Tax Line will look it up for an authorized person, and Letter 147C is the written confirmation to request.

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