Use a Social Security number (SSN) on your federal tax return if you have one or are eligible to receive one. If you are not eligible for an SSN but must provide a U.S. taxpayer identification number for a federal tax purpose, the usual route is an Individual Taxpayer Identification Number (ITIN) issued by the IRS.
These are not interchangeable choices. SSN eligibility controls the decision. An ITIN is a tax-processing number only; it does not provide work authorization, immigration status, or Social Security benefit eligibility.
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The short answer: SSN first, ITIN only when an SSN is unavailable
For an individual, the controlling question is whether the person has, or can obtain, an SSN.
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- You already have an SSN: Put the SSN on your federal return and stop using any ITIN after the Social Security Administration (SSA) issues the SSN.
- You may qualify for an SSN: Resolve eligibility with the SSA and apply there if appropriate. Do not submit Form W-7 for an ITIN while an SSN application is pending.
- You are not eligible for an SSN but have a federal tax reason to identify yourself: Apply to the IRS for an ITIN with Form W-7, following the current instructions.
- You are a spouse or dependent on another person’s return: Being listed alone does not guarantee an ITIN. An allowable tax benefit or a rule requiring the person to file their own return generally must support the application.
The IRS describes ITINs as numbers for people who are not eligible to obtain an SSN but need an identification number for federal tax purposes. The agency’s official video states: “WE ISSUE ITINS TO INDIVIDUALS WHO ARE NOT ELIGIBLE TO OBTAIN A SOCIAL SECURITY NUMBER, OR SSN.”
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SSN and ITIN compared
| Question | Social Security number | Individual Taxpayer Identification Number |
|---|---|---|
| Who issues it? | Social Security Administration | Internal Revenue Service |
| Who generally uses it for an individual tax return? | A person who has or is eligible for an SSN | A person who is not eligible for an SSN but has a qualifying federal tax purpose |
| Application route | SSA application process | IRS Form W-7 and supporting documents |
| Primary function | Social Security identification and, when applicable, tax reporting | Federal tax identification only |
| Does it grant work authorization? | An SSN by itself is not a work permit; work authorization is governed by separate rules | No |
| Does it create immigration status? | No | No |
| Does it create eligibility for Social Security benefits? | An SSN is used in the Social Security system, but benefit eligibility depends on separate rules | No |
| Format | Nine digits | Nine digits |
The similar nine-digit format does not make the numbers interchangeable. The IRS uses the ITIN to process a federal tax obligation when an SSN cannot be issued, while the SSA controls SSN eligibility.
Who commonly needs an ITIN?
IRS examples include people who must file a U.S. return or claim a refund but cannot receive an SSN, resident aliens who must file but are not SSN-eligible, certain spouses or dependents, and some people claiming treaty benefits. These are examples rather than an automatic list. Immigration category alone does not determine tax residency, filing responsibility, or ITIN eligibility.
Nonresident aliens with a U.S. filing obligation
A nonresident alien who must file a U.S. income tax return or file to claim a refund may need an ITIN if the person cannot obtain an SSN. The tax filing requirement and the person’s status under the applicable tax rules still have to be established; simply being outside the United States does not by itself create an ITIN requirement.
Resident aliens who cannot obtain an SSN
A person treated as a resident alien under the relevant residency rules may have to file a federal return. If that individual is not eligible for an SSN, an ITIN can provide the identification number needed for the return.
Spouses and dependents
A spouse or dependent named on someone else’s return does not automatically qualify. IRS guidance ties eligibility to an allowable tax benefit or to the individual filing a return of their own. Gather the facts supporting the specific benefit or filing obligation before preparing Form W-7.
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Treaty-benefit claims
Some people seeking a tax-treaty benefit may use an ITIN when they cannot receive an SSN. The applicable treaty provision, filing position, and W-7 exception documentation determine whether the number is available.
Foreign students and scholars
Students and scholars should not assume an ITIN is automatically correct. IRS guidance explains that people in statuses permitting U.S. employment under specified conditions may be eligible for an SSN. Many F-1, J-1, M-1, and Q-1 students or scholars may qualify when actually employed. Someone who cannot obtain an SSN or cannot satisfy SSA evidence requirements may use the ITIN process when a valid federal tax reason exists.
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The pending-application situation is a common source of mistakes. If you believe you qualify for an SSN, pursue that determination with the SSA first. The current Form W-7 instructions say not to file Form W-7 if you have an SSN or are eligible for one, and not to submit Form W-7 while an SSN application is pending.
If the SSA determines that you are ineligible, the W-7 instructions generally call for documentation of that denial, such as an SSA denial letter, with the ITIN submission. The exact evidence and any exception requirements come from the version of the W-7 instructions that applies when you file.
How to apply for an ITIN
The usual application combines Form W-7, a federal income tax return, and documents proving identity and foreign status. A documented exception can remove the return-attachment requirement in certain cases. Use the latest Form W-7 and its instructions rather than relying on an old form or a generic checklist.
- Confirm that an SSN is not available. If you have an SSN, are eligible for one, or have an SSN application pending, stop and resolve that issue with the SSA. Do not use Form W-7 as a substitute for an SSN application.
- Identify the federal tax purpose. Determine why the applicant needs a taxpayer identification number: a required return, a refund claim, a qualifying spouse or dependent benefit, a treaty position, or another reason listed in the current IRS rules.
- Choose the applicable W-7 category or exception. The form asks for the reason the applicant is requesting an ITIN. If relying on an exception to filing a tax return, collect the specific supporting evidence required for that exception.
- Prepare the federal return when required. In the ordinary process, attach the completed federal income tax return to Form W-7. Do not file the return separately using a blank, missing, or guessed taxpayer number.
- Collect acceptable identity documents. The IRS may require original documents or copies certified by the issuing agency. IRS Topic 857 says notarized copies are not accepted for this purpose. Follow the current instructions for which documents establish identity and foreign status and whether a particular document must be original or agency-certified.
- Complete Form W-7 accurately. Use the applicant’s legal name, mailing information, birth details, country of citizenship, and other information exactly as required. Match the return and evidence to the information on the form.
- Submit the package through an allowed channel. The IRS instructions explain the permitted submission methods and where to send the application. Keep copies of the form, return, and documents, and use a delivery method that lets you document submission when appropriate.
- Respond to IRS correspondence. If the IRS requests missing evidence or clarification, answer using the notice’s instructions. An incomplete response can delay assignment or result in rejection.
Because document rules and exceptions can change, the latest W-7 instructions control over a prior year’s checklist. The December 2024 instructions and the IRS’s related guidance are useful starting points, but confirm that the form version and requirements match the tax year and filing situation.
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Documents and filing exceptions
Identity documentation is a substantive part of the application, not a formality. The IRS may require a document that proves both identity and foreign status, or a combination of documents when one item does not establish both. Original documents or copies certified by the issuing agency may be required; ordinary photocopies and notarized copies do not automatically satisfy the rule.
Most applicants attach a federal return. The W-7 instructions also list exceptions, such as certain third-party reporting, treaty, or other tax-administration situations. Each exception has its own evidence requirements. Do not claim an exception merely because attaching a return is inconvenient; identify the exact exception and provide every document it calls for.
What an ITIN does not provide
An ITIN solves one problem: identifying a person for federal tax administration when an SSN cannot be issued. It does not change the person’s legal status or create unrelated benefits.
- No work authorization: An ITIN is not an employment permit. Employment authorization comes from separate immigration and employment rules.
- No immigration status: Receiving an ITIN does not grant lawful status, a visa, residence, or a path to citizenship.
- No Social Security benefits: An ITIN does not create eligibility for Social Security benefits.
- No automatic access to tax credits: IRS guidance says an ITIN filer is not eligible for the earned income credit. Other credit rules, including child-related credits, vary by tax year and depend on the facts, so check the instructions for the return being filed.
An ITIN also does not make an otherwise nonresident or resident taxpayer meet a different residency test. The number identifies the filer; it does not decide which tax rules apply.
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Using an SSN after an ITIN was issued
If the SSA later issues an SSN, use the SSN on future federal returns and stop using the ITIN. IRS instructions direct taxpayers to notify the IRS so records can be combined where necessary. Continuing to put the old ITIN on a return after an SSN is issued can create duplicate records or mismatched information.
ITIN expiration and renewal
ITINs can expire based on tax-year use. The 2025 edition of IRS Publication 519 says an ITIN that was not used on a federal tax return for tax year 2022, 2023, or 2024 expired on December 31, 2025. A person who needs that number for a 2025 federal return must renew it.
That statement is tied to the 2025 publication and should not be generalized automatically to later filing years. For a later return, check the newest IRS renewal guidance and determine whether the number has expired under that year’s rule. Publication 519 also says renewal is not needed when no federal return is required.
Decision guide by situation
| Your situation | Next action | Why |
|---|---|---|
| You have an SSN | File using the SSN. | The SSN is the individual taxpayer number to use when available. |
| You have never had an SSN and may qualify | Check with the SSA and apply for an SSN if eligible. | An ITIN is not an alternative for someone who can receive an SSN. |
| Your SSN application is pending | Wait for the SSA determination; do not submit Form W-7 meanwhile. | The W-7 instructions prohibit applying for an ITIN while an SSN application is pending. |
| The SSA denied eligibility and you have a federal tax purpose | Prepare Form W-7 with the required denial evidence and tax documents. | The denial supports the position that an ITIN, rather than an SSN, is appropriate. |
| You need a number for a spouse or dependent | Document the allowable tax benefit or own-return requirement. | Listing a person on a return alone is not a universal ITIN qualification. |
| You are a foreign student or scholar | Check whether your employment and status make you SSN-eligible before considering Form W-7. | Many people in F-1, J-1, M-1, or Q-1 situations may qualify for an SSN when actually employed. |
| Your ITIN was not used on returns for 2022, 2023, or 2024 | For a 2025 return, renew it if needed; for later years, check the current rule. | Publication 519 (2025) sets the December 31, 2025 expiration rule for that period. |
Common mistakes and how to avoid them
Applying for an ITIN because getting an SSN seems difficult
Difficulty, delay, or unfamiliarity with the SSA process does not establish ITIN eligibility. If the person may qualify, the correct first step is an SSA determination.
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This conflicts with the W-7 instructions and can lead to a rejected or delayed application. Wait for the SSA decision and retain the denial documentation if the SSA finds the applicant ineligible.
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Assuming immigration category decides the answer
Visa or immigration category can affect SSN eligibility and tax treatment, but it does not by itself answer the filing question. Consider employment authorization, tax residency, filing responsibility, and the evidence required for the particular return.
Using a spouse or dependent’s ITIN without a qualifying reason
The applicant must fit an IRS eligibility rule. A name appearing on another taxpayer’s return is not, by itself, a guaranteed reason for a number.
Sending unacceptable document copies
Ordinary photocopies or notarized copies may fail the IRS standard. Check whether an original or an issuing-agency-certified copy is required and follow the current document list.
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsAssuming an old ITIN remains active forever
Check tax-year use and the latest renewal rules before filing. The 2025 Publication 519 rule demonstrates why an unused number can expire even though it was previously issued.
Expecting an ITIN to unlock credits or benefits
An ITIN is a federal tax identifier, not a benefits card. In particular, IRS guidance excludes ITIN filers from the earned income credit, while other credits require a separate, current-year analysis.
What to check before submitting a return
- Is the taxpayer already assigned an SSN?
- If not, has the SSA determined that the person is ineligible, or is an SSN application still pending?
- Does the person have a current federal tax purpose that supports an ITIN?
- For a spouse or dependent, what exact tax benefit or filing requirement supports eligibility?
- Does the W-7 package include the required federal return or a fully documented exception?
- Are identity and foreign-status documents in an IRS-accepted form?
- Was the ITIN used recently enough to remain active for the return year?
- Are the return’s credits and residency positions being evaluated under the rules for that specific tax year?
Bottom line for filing taxes
The choice is not “whichever number is easier.” Use an SSN when you have one or are eligible for one. If the SSA confirms that you cannot receive an SSN and you have a federal tax reason to provide an identification number, use the IRS ITIN process on Form W-7, with the required return, documents, or exception evidence. Keep the number’s limited purpose in mind: an ITIN supports federal tax filing and does not provide work authorization, immigration status, Social Security benefits, or automatic eligibility for tax credits.
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