Tax ID Number: How To Apply and Look One Up (2026)

A tax ID number is a unique identifier that connects an individual or business with their federal tax records. The IRS or Social Security Administration may issue the number, depending on the taxpayer and purpose.

Every one of the roughly 164 million individual income tax returns the IRS expects for the 2025 tax year needs a correct identification number to file.

This guide explains the main types of tax ID numbers and who needs each one. It also covers where to find a tax ID and how to apply.

What is a tax ID number?

A tax identification number (TIN) is a unique number the IRS uses to administer federal tax laws. It identifies an individual or entity on tax returns, statements, and other tax records. State tax agencies issue separate IDs for state taxes.

There are several types of tax ID numbers:

Social Security number

The Social Security Administration (SSA) issues Social Security numbers (SSNs) to US citizens and eligible noncitizens. An SSN has nine digits in the pattern XXX-XX-XXXX.

Employers use SSNs to report wages, and the IRS uses them to identify individual taxpayers. The SSA also uses the Social Security numbers to record earnings connected to Social Security benefits.

Applying for an original SSN is free. Applicants can request a new Social Security card by completing an online form or Form SS-5 and bringing or mailing the required documents to the nearest Social Security office. They can also use Form SS-5 to request a replacement card.

Individual taxpayer identification number (ITIN)

The IRS issues ITINs to people who need a federal tax ID but aren’t eligible for an SSN. Eligible applicants can include resident aliens, nonresident aliens, and qualifying spouses or dependents. An ITIN has nine digits and always begins with 9.

An ITIN is used for federal tax purposes. It doesn’t qualify the holder for Social Security benefits. It also doesn’t change immigration status or authorize work in the US. Applicants use Form W-7 and provide documents that prove their identity and foreign status.

An ITIN expires after three consecutive tax years with no use on a federal tax return. Renew an expired ITIN if it will appear on a new federal return.

Federal employer tax identification number (EIN)

An EIN is a nine-digit federal tax ID issued by the IRS. It follows the pattern XX-XXXXXXX. The SBA’s federal tax ID guidance explains that an EIN is required to operate a corporation or partnership, file business taxes, hire employees, open bank accounts, and apply for licenses and permits, among other allowances.

Sole proprietors can request an EIN for banking or state tax purposes, though most aren’t required to. The IRS also assigns EINs to certain trusts and estates.

Eligible applicants can apply for an EIN online through the IRS for free. Form SS-4 is available for fax or mail applications.

Adoption tax identification number (ATIN)

An ATIN is a temporary nine-digit number the IRS issues during a pending adoption. It is available when the child is a US citizen or resident and an SSN won’t be ready before the tax filing deadline.

Parents apply through Form W-7A. A child who isn’t a US citizen or resident may require an ITIN through Form W-7.

Preparer tax identification number (PTIN)

Anyone paid to prepare or help prepare a federal tax return must have a valid PTIN. The IRS requires paid preparers to renew their PTIN each year.

An online PTIN application takes about 15 minutes. The application or renewal fee is $18.75. Paper applications use Form W-12 and take about six weeks to process.

State tax ID numbers

State tax authorities issue IDs for state income, employment or sales taxes. Requirements and application steps vary. The SBA directs businesses to the relevant state tax agency for local requirements.

After registering to collect sales tax, Shopify stores can add their state sales tax ID in Shopify admin. Shopify Tax can calculate sales tax at checkout, show state-by-state liability insights, and automate filing and remittance.

Tax ID vs. EIN: What’s the difference?

A tax ID is the umbrella category; an EIN is one specific type of tax ID issued to businesses. The table below breaks down the rest of the differences:

Do you need a tax ID number?

Some businesses, such as sole proprietorships, can operate using their owner’s tax ID. In July 2026, the Bureau of Labor Statistics counted 9.844 million self-employed workers in unincorporated businesses, such as sole proprietorships.

A business may need a separate tax ID when:

• The business hires employees and must pay payroll taxes
• The business is taxed as a partnership or corporation
• A single-member LLC elects corporate or S corporation tax treatment
• The business must file employment or excise tax returns
• The business withholds federal tax on nonwage income paid to a nonresident alien
• The entity is a tax-exempt organization, estate, or certain type of trust
• A state requires an ID for income, employment, or sales taxes
• A bank or licensing agency requests an EIN

Federal tax rules make an EIN optional for some businesses. The IRS allows these businesses to request an EIN for banking or state tax purposes.

Owners use the number when they file small business taxes. They may also claim tax deductions. Filing dates vary by entity type, so check the applicable business tax deadline.

Eligible Shopify store owners can use Shopify Balance to manage business funds from Shopify admin. The financial account can receive Shopify Payments payouts, pay bills, or make business purchases. To be eligible for Shopify Balance, you need a valid US SSN or ITIN for identity verification.

Does an LLC need an EIN?

An LLC needs an EIN when it has more than one owner, hires employees, or elects corporate or S corporation tax treatment. An LLC taxed as a C corporation may also owe corporate income taxes. Relevant excise tax duties can also create an EIN requirement.

A single-member LLC with no employees can generally use the owner’s SSN when it retains its default federal tax classification and has no applicable excise tax duties. The owner can still request an EIN for banking or state tax purposes.

Do you need a tax ID to sell online?

An online business needs a taxpayer identification number for its federal returns. A sole proprietor without employees may be able to use an SSN. A partnership, corporation, or other business that meets the IRS requirements needs an EIN.

Online sellers may also need a state sales tax ID. The requirement depends on where the business must register and collect sales tax. After registering, stores can charge sales tax for their US business. A business may also owe use tax on taxable purchases when the seller did not collect sales tax.

How to get a tax ID number

The application route depends on the type of tax ID and the issuing agency:

• Social Security number. Apply for free through the SSA. Applicants in the US can begin online and then provide their documents at a Social Security office. Form SS-5 is also available.
• Individual taxpayer identification number. Submit Form W-7 with identity documents and proof of foreign status. You can submit applications by mail or through an approved in-person service.
• Adoption tax identification number. File Form W-7A for a US citizen or resident child placed in a pending adoption. An ATIN applies when the child’s SSN won’t be available before the tax return is due.
• Preparer tax identification number. Paid tax preparers can apply or renew online. The paper route uses Form W-12 and takes about six weeks to process.

How to get an EIN

1. Form the business entity. Register an LLC, partnership, or corporation with the appropriate state before requesting an EIN. The IRS recommends completing entity registration first.
2. Prepare the Form SS-4 information checklist. The Form SS-4 instructions request:
   • Legal and trade names
   • Mailing and physical addresses
   • Entity type and reason for applying
   • Responsible party’s name and SSN or ITIN
   • Business start date and accounting year-end
   • Expected employee count and first wage date
   • Principal business activity
3. Choose an application route. Eligible US applicants can apply online through the IRS for free. Approved applicants receive the EIN immediately. US applicants can also send Form SS-4 t by fax or mail, while international applicants can apply by phone, fax, or mail.
4. Submit one application. Use one application method for each entity. Keep a copy of Form SS-4 and the submitted information with the business’s permanent records.
5. Save the CP 575 confirmation letter. The CP 575 confirms your EIN. Eligible Business Tax Account users can download a digital copy. Banks and other institutions accept it as written confirmation of the EIN.

How to look up a tax ID number

Lookup options depend on the type of number and who owns it. SSNs and ITINs identify individuals, so use personal records or the issuing agency. Some EINs appear in public regulatory or nonprofit records.

How to find your own tax ID number

For an SSN, check your Social Security card, a prior federal tax return, Form W-2, or official payroll records. If the card is missing, request a free replacement from the SSA. The SSA verifies your identity before issuing the replacement card.

An ITIN appears on the CP 565 Notice of ITIN Assignment, prior federal tax returns and IRS correspondence. Paid preparers can find their PTIN in the IRS online PTIN account. State tax IDs usually appear on registration certificates, state returns or a state revenue account.

For an EIN, check the original CP 575 notice, prior business tax returns, bank records, payroll records and license applications. A business tax transcript can also confirm the number.

Eligible Business Tax Account users can download a digital CP 575. An authorized person can call the IRS Business and Specialty Tax Line at 800-829-4933 and request Letter 147C. The IRS will verify the caller’s identity and authority.

How to find another company’s EIN

Public search options are limited for private businesses. When there is a legitimate tax or payment purpose, ask an authorized company representative to complete a W-9 form. A payer can use the information to prepare a 1099 form. Store the completed form securely with the company’s vendor tax records.

For a public company, search the Securities and Exchange Commission’s (SEC) database EDGAR by company name or ticker. Open a recent Form 10-K and look for “I.R.S. Employer Identification No.” near the cover page.

For a nonprofit, use the IRS Tax Exempt Organization Search. Search by organization name, city, state, or EIN.

A secretary of state database may show a state entity number. That number is separate from the federal EIN. When a public filing and company-supplied Form W-9 list different numbers, ask the company to confirm the correct TIN before preparing tax forms.