EIN vs SSN vs ITIN: Which Tax ID Goes on Which Form

A client sends you a W-9 and there is a box asking for a taxpayer identification number. You have more than one number and no idea which the form wants. The EIN vs SSN question, with ITIN sitting alongside both, is one of those things nobody explains until you get it wrong.

Disclaimer: This article explains how the IRS describes these numbers and links to the relevant forms. It is general information, not tax advice. For your own situation, consult a tax professional or the IRS directly.

The three numbers, in one paragraph each

SSN, Social Security number. Issued by the Social Security Administration. For individuals, the IRS treats this as your taxpayer identification number by default. It has nine digits in a 000-00-0000 pattern. You apply with Form SS-5 through the SSA rather than through the IRS.

EIN, Employer Identification Number. Nine digits in a 00-0000000 pattern, one hyphen rather than two. It identifies a business entity. Entities that are not individuals generally need one. A sole proprietor needs one in specific circumstances, such as having employees or certain employment and excise tax obligations, and can request one voluntarily otherwise. You apply with Form SS-4, or online through the IRS.

ITIN, Individual Taxpayer Identification Number. The IRS describes it as a nine-digit number issued to individuals who are required to have a US taxpayer identification number for federal tax purposes but who do not have and are not eligible to get an SSN. You apply with Form W-7.

The distinction that actually decides it

Notice what separates them. It is not company against person, which is what most people assume.

SSN and ITIN are alternatives to each other. They occupy the same slot. You have an SSN, or if you are not eligible for one, you have an ITIN. The IRS is explicit that a resident alien who does not have and cannot get an SSN enters the ITIN in the Social Security number space on a W-9.

EIN sits in a different category. It identifies a business entity rather than a human being, which is why a sole proprietor can hold both an SSN and an EIN at once.

What goes on a W-9

The W-9 exists so that somebody who has to file an information return can report what they paid you. The IRS lists the situations:

• income paid to you,
• real estate transactions,
• mortgage interest,
• cancellation of debt,
• contributions to an IRA.

Here are the cases people get stuck on, in the IRS's own terms.

• You are an individual. Your SSN.
• You are a sole proprietor with an EIN. You may enter either your SSN or your EIN. The IRS states a preference for the SSN, which is worth knowing because most people assume the business number is the more correct answer.
• You are a single-member LLC treated as disregarded. Enter the owner's SSN, or the owner's EIN if the owner has one. The IRS says specifically not to enter the disregarded entity's own EIN. This is the single most common error on this form.
• Your LLC is classified as a corporation or a partnership. Now enter the entity's EIN.
• You are not eligible for an SSN. Your ITIN, entered in the SSN space.

Quick tip: If you’re filling one of these out online and not sure what a box wants, Guidy reads the field and tells you what it's asking, right on your screen, without closing the forms and changing tabs.

Why an incorrect number costs money

If you fail to furnish a TIN, or the IRS notifies the payer that yours is wrong, the payer may have to apply backup withholding at 24 percent. It does not reach every kind of payment: which categories are covered depends on the payment type and some are excluded, so what applies to you depends on what you are being paid for.

Where it does apply, it is not a penalty in the usual sense. It is your money held back until the paperwork is right, which for a freelancer waiting on an invoice is much the same thing.

The ITIN expiry trap

This one catches people who did everything correctly years ago.

The IRS states that ITINs not included on a US federal tax return at least once in the last three consecutive tax years expire. An expired ITIN can still be used on a W-9, but it has to be renewed before it will work on a tax return without processing delays.

Two other points the IRS makes about ITINs. Applicants must show a federal tax purpose, usually by attaching a federal tax return to the W-7. And a taxpayer or spouse holding an ITIN is not eligible for the Earned Income Tax Credit, even where dependents hold valid SSNs.

Do you actually need an EIN?

Not every sole proprietor does.

The requirement turns on specific circumstances rather than on being in business at all. Having employees is the clearest trigger, and certain employment and excise tax obligations also require one. An entity that is not an individual generally needs one regardless. A freelancer with no employees, operating under their own name, often has no federal requirement to hold one.

Requesting one anyway is allowed, and holding an EIN does not by itself create a filing obligation. Filing obligations come from the underlying activity rather than from the number.

There is still an argument for getting one. An EIN on a W-9 keeps your Social Security number off a document that goes to every client you invoice, which is a privacy benefit rather than a tax one. That is a reasonable thing to want, and it is a different question from whether the IRS requires it.

Where the number goes after you hand it over

The W-9 is not the destination. It is how the payer gets the number they need for an information return, which is the form reporting to the IRS what they paid you. The number you put on the W-9 is the number that appears there, which is why a mismatch surfaces months later as a letter rather than immediately as an error.

That is the practical argument for getting it right the first time. A W-9 takes two minutes. Correcting an information return that carried the wrong identification number involves the payer, the IRS, and a timeline you do not control.

Keep a copy of every W-9 you send, with the date and the number you used on it.

A fourth number, briefly

You may see ATIN on a form's instructions. It is an adoption taxpayer identification number, applied for on Form W-7A, used for a child being adopted where an SSN is not yet available. It is rare, and it is not an alternative to any of the three above.

Key takeaways

• The EIN vs SSN question is not business against person: SSN and ITIN are alternatives to each other, and an EIN identifies an entity
• An ITIN is only for people who are required to have a US taxpayer identification number and are not eligible for an SSN
• A sole proprietor holding both may put either on a W-9, and the IRS states a preference for the SSN
• A single-member LLC treated as disregarded uses the owner's number, not the entity's EIN
• An incorrect or missing number can trigger backup withholding at 24 percent on covered payment types until it is corrected

FAQs

Can one person hold all three numbers?

Not all three. SSN and ITIN are mutually exclusive, since an ITIN is issued only to people not eligible for an SSN. Someone can hold an SSN and an EIN, or an ITIN and an EIN.

Which form do I use to apply for each?

Form SS-5 for an SSN, through the Social Security Administration rather than the IRS. Form W-7 for an ITIN. Form SS-4 for an EIN, which the IRS also accepts online.

Does an EIN keep my Social Security number private?

On the forms where you are permitted to use it, yes, and that is a legitimate reason to have one. It does not change your tax treatment, and it does not apply where the IRS requires the owner's own number, such as a disregarded single-member LLC.

How do I tell an EIN from an SSN by looking at it?

By the hyphens. Both have nine digits. An SSN carries two hyphens in a 000-00-0000 pattern and an EIN carries one, in a 00-0000000 pattern.

What if I am waiting on a number when a client asks for the form?

The W-9 certification does allow for having applied and being awaiting a number, so returning the form beats leaving it unanswered. Do not assume that protects the payment, though.

The awaiting-TIN treatment that suspends withholding for a period applies to interest, dividends and certain tradable instruments rather than to everything, and nonemployee compensation can be subject to backup withholding straight away even where you have applied. If a payment is imminent, ask the payer what they intend to do and speak to a tax professional.

Tax forms are short, and each field assumes a piece of knowledge nobody hands you. Guidy reads the form on your screen and explains what a box is asking before you fill it in, which is different from filling it in for you. Our AI form filler page covers where that fits.