There are several instances when you would need to apply for a federal employer identification number (EIN). The most common instance is when you are operating a business and you have employees. If you are operating a sole proprietorship and you do not have any employees, your social security number is typically all you need.
If you are a sole proprietor and you have an EIN, you’ll need to get a new one if you convert to a partnership or corporation. If you convert to a limited liability company, you’ll only need a new EIN if you choose to be taxed as a corporation or partnership.
You won’t need a new EIN if you only change the name or location of your business, or if you operate at more than one business location.