A Tax ID Number Is 9 Digits Long, No Matter Which Type You Have

Every tax identification number issued in the United States is exactly 9 digits long. Whether you are a sole proprietor with an Employer Identification Number (EIN), a business partnership, a corporation, or a nonprofit organization, the format is always the same: nine digits, typically written as XX-XXXXXXX (with a hyphen after the first two digits, though the hyphen is not part of the number itself).

Your Social Security Number also serves as a tax ID if you are self-employed and do not have a separate EIN. A Social Security Number is also 9 digits, written as XXX-XX-XXXX. The IRS uses whichever number you provide on your tax return to track your income and filing history.

The length never changes, regardless of how many employees you have, how long your business has been operating, or whether you are filing federal, state, or local taxes. A new business and a 50-year-old corporation both use 9-digit numbers.

Key Takeaways

  • All U.S. tax ID numbers are exactly 9 digits long, whether they are EINs or Social Security Numbers.
  • An EIN is formatted as XX-XXXXXXX (two digits, hyphen, seven digits), but the hyphen is only for readability and is not part of the actual number.
  • If you are self-employed without employees, you can use your Social Security Number as your tax ID instead of requesting an EIN.
  • The IRS does not issue shorter or longer tax ID numbers; if a number you received is not 9 digits, it is not a valid tax ID.

Why the Format Is Always 9 Digits

The IRS standardized the 9-digit format decades ago to create a unique identifier for every taxpayer, business, and organization. Nine digits provide roughly one billion possible combinations, which is enough to cover all current and foreseeable future tax entities in the United States.

The first two digits of an EIN carry meaning — they indicate the state where the business was formed or the type of entity (nonprofit, trust, estate, and so on). The remaining seven digits are assigned sequentially by the IRS. However, you do not need to decode these digits yourself; the IRS uses them internally for sorting and tracking.

Social Security Numbers follow a different historical pattern (the first three digits originally indicated the state where the number was issued), but they are still 9 digits for the same reason: to create a unique identifier that works across all federal systems.

How to Verify Your Tax ID Number Is Correct

Count the digits in your number. If you have an EIN, it should be 9 digits with a hyphen in the middle: for example, 12-3456789. If you are using your Social Security Number, it should be 9 digits with hyphens in the format XXX-XX-XXXX, such as 123-45-6789.

If you received a number that is shorter or longer than 9 digits, or if it contains letters, it is not a valid tax ID. Contact the IRS or the organization that issued it to confirm you have the correct number. A mistyped or incomplete tax ID can cause your return to be rejected or delayed.

When you file your tax return, the IRS will cross-check your tax ID number against their records. If the number does not match the name on your return, the IRS will contact you to correct it before processing your return.

Where to Find Your Tax ID Number

If you have an EIN, it appears on the IRS letter you received when you first requested it (Form SS-4). That letter is usually titled "Notice of Approval" or "EIN Assignment Notice" and was mailed to you at the address you provided. Keep this letter in your records.

If you cannot find the original letter, you can look up your EIN on the IRS website using the IRS EIN Lookup tool, or you can call the IRS Business and Specialty Tax Line at 1-800-829-4933. Have your business name, address, and the responsible party's Social Security Number ready when you call.

If you are using your Social Security Number as your tax ID, you already know it — it is the same number on your Social Security card. If you have lost or forgotten your Social Security Number, contact the Social Security Administration at 1-800-772-1213.

What Happens If You Use the Wrong Tax ID Number

Filing your tax return with an incorrect or incomplete tax ID number can cause several problems. The IRS may reject your return outright, delay processing it while they try to match the number to your records, or assign your income to the wrong taxpayer account.

If your income is reported under the wrong tax ID, you may not receive credit for taxes withheld from your paychecks, and you could end up owing money when you file. The IRS will eventually catch the error and contact you, but correcting it takes time and can delay your refund.

To avoid this, double-check your tax ID number before you file. Compare it digit by digit against the official document (your EIN approval letter or Social Security card). If you are filing through a tax professional or software, they will usually catch a mismatched number, but it is your responsibility to provide the correct one.

EIN vs. Social Security Number as a Tax ID

If you are self-employed and work alone (a sole proprietor with no employees), you can use your Social Security Number on your tax return instead of getting an EIN. Both are 9 digits, and both work with the IRS.

However, if you hire employees, operate as a partnership, form a corporation, or run a nonprofit, you must have an EIN. You cannot use a Social Security Number for these entity types. An EIN is free to request from the IRS and takes about 15 minutes to explore for online.

Some sole proprietors choose to get an EIN anyway, even though they are not required to, because it separates their personal tax ID from their business tax ID. This can make accounting simpler and provides a small layer of privacy when dealing with vendors and clients.

Frequently Asked Questions

Can a tax ID number be longer or shorter than 9 digits?

No. The IRS only issues 9-digit tax ID numbers. If you have received a number that is not 9 digits, it is not a valid tax ID. Contact the IRS or the organization that issued it to request the correct number.

Does the hyphen in an EIN count as part of the 9 digits?

No. The hyphen is only for readability. The actual tax ID number is 9 digits: the first two, then the last seven. When you enter your EIN into online forms or software, you may be asked to enter it with or without the hyphen — both are correct.

What if I have both a Social Security Number and an EIN?

You can have both. If you are self-employed and also run a business with employees, you will use your EIN on business tax returns and your Social Security Number on personal tax returns. The IRS tracks both and links them to your overall tax account.

Is my tax ID number the same as my account number with the IRS?

Your tax ID number is your account number with the IRS. It is the identifier the IRS uses to store all your tax records, filing history, and payment information. There is no separate account number.

What should I do if I lose my EIN?

You do not need to request a new EIN. Your EIN never changes. Look up your existing EIN using the IRS EIN Lookup tool on the IRS website, or call the IRS Business and Specialty Tax Line at 1-800-829-4933. Keep the number in a safe place for future reference.