A woman business owner stands in a bright, modern kitchen. She has papers before her. She is reviewing and filling out a form.
If you need to correct a mistake in your employer identification number (EIN), request a new one, or find a missing EIN, this step-by-step guide will help you through the process. — Getty Images/jacoblund

The IRS uses an employer identification number, or EIN, to identify a business entity. This unique nine-digit number is like a Social Security number for companies. Not all businesses need an EIN, but if you have employees or formed as a corporation or partnership, you need to apply for an EIN. The IRS offers EINs for free, and you can get your EIN immediately after completing the online application prompts.

You may need to change your EIN at some point in your business's life cycle. Contrary to what you might expect, you can't actually change your EIN. It's designed to be a permanent identifier for your business (again, much like a Social Security number). However, you can either correct mistakes in an existing EIN or get a new EIN depending on your business situation.

When to get a new EIN

The rules for acquiring a new EIN vary according to the type of business entity. For instance, sole proprietors do not need to apply for a new EIN if they are changing the name of their business or changing their location/adding new locations.

However, if a corporation goes through a statutory merger resulting in a name change, it will need a new EIN. The IRS has a helpful one-pager breaking down events that require an EIN change.

Here's a good rule of thumb: If your business name changes, but your structure (sole proprietorship, LLC, etc.) remains the same, you generally don't need a new EIN. However, you should notify the IRS of the name change.

The IRS recommends doing this in writing on company letterhead, if available. Include your current EIN, the new business name, and your contact information.

"If you change your address or you change the responsible party for your business you must use Form 8822-B, Change of Address or Responsible Party – Business to notify the IRS of your new address. You must report this change within 60 days," wrote The Balance.

If your business undergoes a significant change, such as converting from a sole proprietorship to an LLC, you might need a new EIN. The IRS advises consulting with a tax professional for guidance in this situation.

[Read more: How to Establish and Build Business Credit]

The IRS offers EINs for free, and you can get your EIN immediately after completing the online application prompts.

How to change an incorrect EIN

Don't submit a new application if you made a mistake on your original EIN form. Instead, send a letter to the IRS explaining the error and providing the correct information. This letter should be signed by an authorized representative of your company and include your current EIN.

[Read more: A Complete Guide to Filing Your Business Taxes]

What to do if you lose/misplace an EIN

In the unfortunate event that you misplace an EIN, there are a few options you can try to find it. You would have needed your EIN to open a bank account or to apply for a state or local business license.

Contact either your bank or the licensing agency to see if they have your EIN on file. You also need your EIN to file a tax return. Look at previous tax filings to find your EIN.

There is a toll-free number you can call if none of these options is available. The IRS's Business & Tax Speciality Line is available at 800-829-4933. Have the authorized person for your business call the number and verify their identity to receive your EIN.

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