Learn About Finding Your Tax Identification Numbers

Understanding Tax Identification Numbers and Why You Need Them

A tax identification number is a unique code assigned by the Internal Revenue Service (IRS) to identify individuals and businesses for tax purposes. If you earn income in the United States, you will likely need one of these numbers to file taxes, open a bank account, or conduct business. The most common type is the Social Security Number (SSN), which nine out of ten Americans hold. However, other types exist depending on your situation and work status.

The IRS uses these numbers to track your income, monitor tax compliance, and maintain records of payments throughout your lifetime. When employers, banks, investment firms, and other financial institutions receive money related to you, they report this information to the IRS using your tax identification number. This creates a permanent record that follows your tax history.

Understanding which number you need is the first step in managing your tax affairs. The wrong identification number—or missing information—can cause delays in processing tax returns, result in incorrect tax records, or create complications when you try to open financial accounts. Many people discover they need a different type of number only after attempting to file taxes or start a business.

Tax identification numbers serve several practical functions beyond taxes. Landlords often request them before renting an apartment. Lenders want them before issuing loans. Schools may ask for them to report scholarship or grant information. Understanding your options prevents confusion in these common situations.

Practical takeaway: Identify which tax identification number applies to your situation before you need it for employment, banking, or tax filing purposes.

The Social Security Number: America's Primary Tax Identifier

The Social Security Number (SSN) remains the primary tax identification number for U.S. citizens, permanent residents, and certain temporary workers. Issued by the Social Security Administration, this nine-digit number has been in use since 1936. According to Social Security Administration data, over 453 million SSNs have been issued throughout American history. For most people who work and earn income in the United States, obtaining an SSN is necessary.

The SSN consists of three parts: the area number (first three digits), the group number (middle two digits), and the serial number (last four digits). Originally, these numbers were geographically coded, meaning the area number indicated where you applied for the SSN. This system changed in 2011 to randomize the number assignment, making it impossible to determine location or application details from the digits alone.

U.S. citizens born in the country typically receive an SSN automatically through hospital records when they are born, or they can request one through the Social Security Administration. Immigrants and refugees who become permanent residents can apply for an SSN through Social Security field offices. Temporary workers on visas may also receive SSNs depending on their visa category and work authorization status.

The SSN serves multiple functions beyond taxes. It appears on your driver's license in many states, on medical records, on employment forms, and in financial accounts. Protecting your SSN is critically important because it can be used for identity theft. You should never share your SSN unless you have confirmed the organization requesting it actually needs it for legal or tax purposes. Banks, employers, and government agencies do have legitimate reasons to request it, but telemarketers and unknown callers generally do not.

Practical takeaway: If you are a U.S. citizen or authorized worker without an SSN, contact your local Social Security Administration office to learn about obtaining one.

The Employer Identification Number for Businesses and Self-Employment

An Employer Identification Number (EIN) is a nine-digit code assigned by the IRS to businesses, nonprofits, trusts, estates, and other entities that have a tax reporting obligation. Unlike the SSN, which identifies individuals, an EIN identifies a business entity. If you start a business, form a partnership, or create a corporation, you will likely need an EIN. According to IRS data, approximately 33 million EINs have been issued to active businesses across the United States.

Self-employed individuals operating as sole proprietors may or may not need an EIN, depending on their specific situation. If you operate a business by yourself without hiring employees, you can often use your Social Security Number for tax reporting purposes. However, many self-employed people choose to obtain an EIN anyway for privacy and business separation reasons. This is particularly common among freelancers, consultants, and small business owners who want to keep business finances distinct from personal finances.

The EIN application process differs from the SSN process. You can apply for an EIN through the IRS website, by mail, by phone, or in person at an IRS office. The IRS offers online application through its EIN Assistant tool, which provides immediate confirmation of your EIN if you apply during business hours. The process takes only a few minutes and does not cost anything. If you apply by mail, processing typically takes four to six weeks. Phone applications, completed through an IRS representative, provide your EIN the same day.

Once you obtain an EIN, you must use it on all business tax returns, payroll tax documents, and when opening business bank accounts. Banks require an EIN to set up business checking accounts separate from personal accounts. This separation is important for accounting purposes and makes it easier to track business income and expenses. If you hire even one employee, an EIN is required by law, not optional.

Practical takeaway: If you plan to start a business or hire employees, apply for an EIN through the IRS website before opening business bank accounts or hiring staff.

Individual Taxpayer Identification Numbers for Non-Citizens and Residents

An Individual Taxpayer Identification Number (ITIN) is a nine-digit tax processing number issued by the IRS to individuals who do not have and are not authorized to obtain a Social Security Number but still have a U.S. tax filing or reporting requirement. ITINs were created in 1996 to serve immigrants, visa holders, and other non-citizens who earn income in the United States. The IRS has issued millions of ITINs to individuals in this situation.

Several categories of people may need an ITIN. Nonresident aliens with U.S. source income typically need one. Visa holders such as H-1B temporary workers, F-1 students with on-campus employment, and J-1 exchange program participants may need one if they have U.S. income. Undocumented immigrants who work and earn income in the United States can obtain an ITIN to file tax returns and report income to the IRS. Spouses of U.S. citizens who do not have work authorization may need one to file joint tax returns. Children of nonresidents may need one to report investment income or educational benefits.

The ITIN format resembles the SSN—it is also nine digits—but it always begins with the number 9 in the area code (first three digits). This distinguishing feature helps the IRS identify the number as an ITIN rather than an SSN. When you look at tax documents or financial records, you can identify an ITIN by this pattern. The IRS issues ITINs through mail-in application only. You cannot apply for an ITIN online or by phone. The application process requires specific documentation proving your identity and residency status, which varies depending on your country of origin and visa category.

One important thing to understand about ITINs is that they are tax numbers only. Holding an ITIN does not grant immigration status, work authorization, or legal residency. It is simply a tool for tax reporting. Some organizations incorrectly assume that having an ITIN means someone has authorization to work in the United States. This is not true. An ITIN allows you to file taxes and report income; it says nothing about your legal status to work or live in the country.

Practical takeaway: If you are not a U.S. citizen or permanent resident but earn income in the United States, investigate whether you need an ITIN by reviewing IRS publication 519 or contacting a tax professional.

Specialized Tax Numbers for Specific Situations

Beyond SSNs, EINs, and ITINs, several other specialized tax identification numbers exist for particular circumstances. Understanding when you might need these numbers prevents confusion during tax season or when conducting specific transactions. Each type serves a distinct purpose within the tax system.

The Adoption Taxpayer Identification Number (ATIN) is a temporary identification number issued to adoptive parents for a child who will be adopted but for whom an