Tax ID numbers have different lengths depending on the type

A Tax ID (also called an Employer Identification Number or EIN) is a nine-digit number assigned by the Internal Revenue Service. If you are a sole proprietor with no employees, you may use your Social Security Number instead, which has nine digits as well. The format is always XX-XXXXXXX, with a hyphen after the first two digits.

The nine-digit structure is standard across all federal tax identification numbers used for business purposes. Whether you are registering a corporation, partnership, LLC, or nonprofit organization, the IRS will issue you a nine-digit EIN if you request one.

Key Takeaways

  • An EIN is always nine digits long, formatted as XX-XXXXXXX with a hyphen after the second digit.
  • Sole proprietors without employees can use their nine-digit Social Security Number as their tax ID instead of requesting an EIN.
  • The IRS assigns EINs to businesses, nonprofits, trusts, and other entities that need a separate tax identification number.
  • You will need your nine-digit tax ID when filing tax returns, opening a business bank account, or hiring employees.

When you need an EIN instead of your Social Security Number

If you operate as a sole proprietor and have no employees, the IRS allows you to use your Social Security Number on your tax return. However, many sole proprietors request an EIN anyway to keep their personal and business finances separate on tax documents.

You must obtain an EIN if you are forming a partnership, corporation, LLC, S corporation, or nonprofit organization. You also need an EIN if you hire employees, operate a business that requires a license (like a daycare or food service operation), or plan to open a business bank account under a business name rather than your personal name.

Where to find your nine-digit tax ID

If the IRS assigned you an EIN, you received a letter (Form SS-4) in the mail that displays your nine-digit number. Keep this letter in a safe place—you will need the number for tax filings, payroll setup, and business banking.

If you cannot locate your original letter, you can call the IRS Business and Specialty Tax Line at 1-800-829-4933 during business hours. Have your business name, address, and the approximate date you received the EIN ready. The IRS can confirm your nine-digit number over the phone.

How the nine digits are organized

The first two digits of an EIN identify the state where the business is located or where the principal office is situated. The remaining seven digits are assigned sequentially by the IRS. The hyphen between the second and third digit is required formatting but is not part of the actual number—all nine digits are what the IRS uses to identify your business.

When you write your EIN on forms, checks, or tax documents, always include the hyphen in the XX-XXXXXXX format. Some computer systems may accept the number without the hyphen, but the standard format includes it for readability and consistency across government and financial institutions.

Using your tax ID on different documents

Your nine-digit tax ID appears on your federal income tax return (Form 1040-C for sole proprietors, Form 1120 for corporations, or Form 1065 for partnerships). It also goes on W-2 forms you issue to employees, 1099 forms for contractors, and quarterly estimated tax payment vouchers.

When you open a business bank account, the bank will ask for your nine-digit EIN. If you are hiring employees, you will provide your EIN to set up payroll withholding with the IRS. Vendors and clients may also request your EIN for their own record-keeping purposes.

What happens if you lose or forget your tax ID

Losing track of your nine-digit EIN is not uncommon, especially if you received it years ago and have not used it recently. The IRS can look up your number if you provide your business name, address, and the year the EIN was issued. You do not need to request a new one—the same nine-digit number remains yours for as long as your business exists.

If you cannot remember any details about when or where you obtained the EIN, contact the IRS directly. They maintain records of all assigned numbers and can confirm whether an EIN was ever issued to your business name and address. This lookup service is available by phone during business hours.

Frequently Asked Questions

Is a tax ID the same as a Social Security Number?

Not exactly. A Social Security Number is nine digits and can be used as a tax ID by sole proprietors. An EIN is also nine digits but is assigned to businesses and organizations. They serve the same purpose on tax forms, but an EIN keeps your personal and business finances separate.

Can a tax ID have fewer or more than nine digits?

No. Federal tax IDs assigned by the IRS are always nine digits. If you see a number that is longer or shorter, it may be a state tax ID, which varies by state, or it may be formatted incorrectly.

Do I need to renew my nine-digit tax ID?

No. Once the IRS assigns your nine-digit EIN, it does not expire and does not need to be renewed. You keep the same number for the life of your business unless the business structure changes significantly.

What if my business has multiple locations?

Your business has one nine-digit EIN regardless of how many locations you operate. You do not receive a separate EIN for each office or store. All locations file under the same nine-digit number.