Who Needs a TIN Number: SSN, ITIN, EIN, ATIN, and PTIN

If you earn income, run a business, settle an estate, adopt a child, or get paid to prepare tax returns in the United States, you need a Taxpayer Identification Number. The IRS recognizes five types, and which one applies to you depends on your situation: a Social Security Number (SSN) for most citizens and authorized residents, an Individual Taxpayer Identification Number (ITIN) for people who owe U.S. tax but can’t get an SSN, an Employer Identification Number (EIN) for businesses and other entities, an Adoption Taxpayer Identification Number (ATIN) for children in the process of being adopted, and a Preparer Tax Identification Number (PTIN) for anyone paid to prepare federal returns.¹

Most people only ever need one. A few situations, like running a business while also filing a personal return, mean holding two at once.

If You Have a Social Security Number

For U.S. citizens and authorized residents, the SSN is the TIN. The Social Security Administration issues it, and the IRS uses it to track your wages, investment income, and tax filings.¹ If you already have one, nothing else is required for a personal return. The remaining four types exist for people and entities that either can’t get an SSN or need a separate identifier for a specific tax purpose.

If You Owe U.S. Tax but Can’t Get an SSN

You need an ITIN if you have a federal tax obligation but aren’t eligible for a Social Security Number. The IRS issues ITINs to nonresident aliens who earn U.S.-source income, resident aliens who meet the substantial presence test, and spouses or dependents of U.S. citizens or resident aliens who need to appear on a return.² Nonresident aliens claiming a tax treaty benefit and foreign students filing a U.S. return also fall in this group.

The substantial presence test asks whether you’ve been physically in the United States for at least 31 days during the current year and 183 days across a three-year window, with the prior year counted at one-third and the year before that at one-sixth.³ Meeting it makes you a resident alien for tax purposes, which means an ITIN is required to file.

One boundary worth knowing: an ITIN doesn’t unlock every credit an SSN does. Through 2025, the Child Tax Credit required the qualifying child to have an SSN specifically. An ITIN-holder dependent may still qualify for the $500 Credit for Other Dependents if the dependent is a resident alien or U.S. national.²⁴

ITINs also expire. If yours doesn’t appear on a federal tax return for three consecutive tax years, it expires on December 31 after that third year of non-use.⁵ Filing with an expired ITIN can delay any refund until the renewal processes.

If You Run a Business or Other Entity

Any business that hires employees needs an EIN, no matter how small. Corporations and partnerships need one even without employees, because they file entity-level returns. A sole proprietor without employees can generally use their SSN, but a separate EIN is required if the proprietor sets up a retirement plan, operates as a nonprofit, or files excise tax returns.⁶ Beyond taxes, the EIN is what banks ask for when you open a business account, and it’s the number that goes on W-2s issued to workers.

The application asks for a “responsible party,” meaning the person who ultimately controls the entity or its assets, and that person supplies their own SSN or ITIN so the IRS can tie the business back to an individual.⁶ If the responsible party later changes, the business has 60 days to report the change on Form 8822-B.⁷

When You Need a New EIN Rather Than Your Existing One

Certain structural changes make the IRS treat your business as a new taxpayer, which means a new EIN. Common triggers include a sole proprietor incorporating, forming a partnership, or filing bankruptcy; a corporation receiving a new charter from the secretary of state, converting to a partnership or sole proprietorship, or merging into a new corporation; a partnership incorporating, dissolving and starting fresh, or collapsing so one partner continues as a sole proprietor; and an LLC terminating and becoming a new corporation or partnership, or a single-member LLC becoming required to file employment or excise taxes.⁸

Simply changing your business name, address, or adding a new partner to an existing partnership does not require a new EIN.⁸

If You’re Handling an Estate or a Trust

When someone dies, the assets they leave behind become a separate taxable entity. The deceased person’s SSN can no longer be used for income the assets generate after death, so the executor or administrator applies for an EIN in the estate’s name and uses it to report interest, dividends, rental income, and capital gains during probate.⁹ An estate with more than $600 in gross income during a tax year files Form 1041.¹⁰

Trusts follow a similar logic. A revocable living trust with a single grantor can use the grantor’s SSN during the grantor’s lifetime, because the IRS treats the trust’s income as the grantor’s income. Once the grantor dies, the trustee must apply for an EIN and begin filing Form 1041 as an ordinary trust.¹¹ Irrevocable trusts that aren’t treated as grantor trusts need their own EIN from the start, because they’re independent entities for federal tax purposes.¹⁰

If You’re Adopting a Child

Adoptive parents sometimes can’t get an SSN for a child until the adoption is finalized. An ATIN bridges the gap. It’s a temporary nine-digit number that lets prospective parents claim the child as a dependent while the legal process plays out, and it works for both domestic and foreign adoptions.¹² A foreign-born child must have a permanent resident card or certificate of citizenship to qualify.¹³

An ATIN automatically deactivates two years after it’s issued, and the IRS sends a reminder at the eighteen-month mark. If the adoption still isn’t final, you can request an extension using Form 15100.¹⁴ Once the adoption is finalized, apply for the child’s SSN and stop using the ATIN on future filings.¹²

If You Prepare Tax Returns for Pay

Anyone who prepares or helps prepare federal tax returns for compensation must have a valid PTIN before touching a return. That includes enrolled agents.¹⁵ The rule comes from 26 U.S.C. § 6109(a)(4), which requires every return prepared by a paid preparer to carry that preparer’s identifying number.¹⁶ The PTIN renews each filing season.¹⁷

Volunteers don’t need one. If you prepare returns for free through a program like VITA, the PTIN requirement doesn’t apply. Compensation is what triggers it.

What Happens if a TIN Is Missing or Misused

Leaving a correct TIN off a return or information document carries a penalty of $50 per failure, up to $100,000 in a single calendar year.¹⁸ For a business filing hundreds of information returns, that adds up quickly.

Deliberately misusing someone else’s TIN is a different order of problem. Federal law treats a taxpayer identification number as a “means of identification,” and using another person’s TIN to commit fraud can result in up to five years in prison. If the fraud yields $1,000 or more in a single year, the maximum sentence rises to fifteen years. Offenses connected to drug trafficking or violent crime carry up to twenty years, and fraud tied to terrorism up to thirty.¹⁹

1
Internal Revenue Service. Taxpayer Identification Numbers (TIN)
2
Internal Revenue Service. Individual Taxpayer Identification Number (ITIN)
3
Internal Revenue Service. Substantial Presence Test
4
Taxpayer Advocate Service. Legislative Recommendation 57 – Clarify Whether Dependents Are Required to Have Taxpayer Identification Numbers for Purposes of the Credit for Other Dependents
5
Internal Revenue Service. How to Renew an ITIN
6
Internal Revenue Service. Instructions for Form SS-4, Application for Employer Identification Number (EIN)
7
Internal Revenue Service. About Form SS-4, Application for Employer Identification Number (EIN)
8
Internal Revenue Service. When to Get a New EIN
9
Internal Revenue Service. Responsibilities of an Estate Administrator
10
Internal Revenue Service. Instructions for Form 1041 and Schedules A, B, G, J, and K-1 (2025)
11
Internal Revenue Service. File an Estate Tax Income Tax Return
12
eCFR. 26 CFR 301.6109-3 – IRS Adoption Taxpayer Identification Numbers
13
Internal Revenue Service. Instructions for Form W-7A
14
Internal Revenue Service. Adoption Taxpayer Identification Number
15
Internal Revenue Service. PTIN Requirements for Tax Return Preparers
16
Office of the Law Revision Counsel. 26 U.S. Code 6109 – Identifying Numbers
17
Internal Revenue Service. IRS Reminds Tax Pros to Renew PTINs
18
Office of the Law Revision Counsel. 26 U.S. Code 6723 – Failure to Comply With Other Information Reporting Requirements
19
Office of the Law Revision Counsel. 18 U.S. Code 1028 – Fraud and Related Activity in Connection With Identification Documents, Authentication Features, and Information