EIN Guide for Your Wisconsin LLC

An Employer Identification Number, or EIN, is a nine-digit number the Internal Revenue Service assigns to a business. It is the business equivalent of a Social Security number — a unique federal identifier used on tax filings, bank paperwork, and payroll. It is sometimes called a Federal Tax Identification Number, but EIN is the common term.

The EIN is federal, not a Wisconsin item. It comes from the IRS and works the same for a Wisconsin LLC as it does for one in any other state. But because nearly every Wisconsin LLC needs one to function — to open a bank account, hire, or file certain returns — it is a core part of setting the company up, and it pairs with your DFI formation to make the LLC operational.

What you use it for

• Opening a business bank account — almost every bank requires an EIN for an LLC account.
• Filing federal taxes — multi-member LLCs and LLCs that elected corporate treatment file returns under the EIN.
• Hiring employees — you need an EIN to run payroll, withhold taxes, and file employment tax returns.
• Registering for Wisconsin taxes — the Department of Revenue generally wants your EIN when you register for a seller's permit or withholding.
• Establishing business credit and vendor accounts — many vendors and lenders ask for it.

Whether you are strictly required to have one depends on your LLC's structure and activities, but in practice most owners should get one regardless.

You are required to have an EIN if

• Your LLC has more than one member. A multi-member LLC is taxed as a partnership by default and must file a partnership return, which requires an EIN.
• You have employees. Payroll and employment tax filings require an EIN.
• You have elected corporate tax treatment (S-corp or C-corp) for the LLC.
• You owe certain federal excise taxes or meet other specific IRS triggers.

Single-member LLCs with no employees

A single-member LLC with no employees is technically allowed to use the owner's Social Security number for federal income tax purposes, because the IRS treats it as a disregarded entity. But nearly every advisor recommends getting an EIN anyway. It keeps your SSN off business paperwork, vendor forms, and bank documents, and most banks will not open a business account without one. Getting an EIN is free and fast, so there is little reason to rely on your SSN.

The IRS issues EINs directly, at no charge. The most important rule: apply at the official IRS website and never pay a third party whose only service is getting you the number the IRS gives away for free.

The online application (fastest)

Apply through the IRS EIN Assistant at IRS.gov. The online application is the fastest route by far:

• It is available during the IRS's posted hours (generally weekday business hours, Eastern time).
• It takes about ten minutes to complete in one sitting — the session does not save, so have your information ready.
• The EIN is issued immediately at the end. You can download the confirmation letter and start using the number the same day.

To apply online, the responsible party completing the application needs a valid U.S. Social Security number or ITIN.

What you will need

• The LLC's exact legal name as it appears on your filed Wisconsin Articles of Organization
• The LLC's mailing address
• The name and SSN or ITIN of the responsible party — generally a member who controls the LLC
• The number of members and the reason you are applying
• The state where the LLC was formed (Wisconsin) and the date of formation

Timing tip

Form your LLC with the DFI first, then apply for the EIN. Applying under the exact legal name on your filed Articles keeps everything consistent and avoids a mismatch between your IRS records and your Wisconsin registration.

If the responsible party does not have a U.S. Social Security number or ITIN, you cannot complete the online application, but you can still get an EIN — it just takes longer.

Apply by fax or mail with Form SS-4

Complete IRS Form SS-4, the Application for Employer Identification Number, and submit it by fax or mail to the IRS. This is the standard route for non-U.S. residents forming a Wisconsin LLC who do not have an SSN or ITIN.

• Fax is faster than mail — the IRS typically returns the EIN by fax within a few business days if you provide a return fax number.
• Mail works but takes considerably longer, often several weeks.

On Form SS-4, non-U.S. applicants without an SSN or ITIN can generally write "Foreign" in the space for the responsible party's tax ID, following the current IRS instructions. Because the IRS updates its procedures periodically, read the SS-4 instructions on IRS.gov before filing so you use the current method.

Do not overpay for help

There are legitimate services that will complete and submit Form SS-4 on your behalf, which can be worth it for a non-U.S. founder navigating the process for the first time. But the EIN itself is always free from the IRS — you are only ever paying for someone's time and handling, never for the number.

Once the EIN is issued, it is permanent and tied to your LLC. A few things follow naturally.

Keep the confirmation letter

Save the IRS confirmation (the CP 575 for new EINs, or the online confirmation letter). Banks and agencies frequently ask for it, and requesting a replacement later is slower than keeping the original.

Open your business bank account

With your filed Wisconsin Articles of Organization and your EIN in hand, you can open a business bank account — the practical step that lets you keep company and personal finances separate, which is essential to preserving the LLC's liability shield.

Register for Wisconsin taxes if needed

If you sell taxable goods or services, or you will have employees, register with the Wisconsin Department of Revenue — your EIN is part of that registration. This is a state step that follows the federal EIN, not a substitute for it.

How Mainstay Filing helps

As part of forming your Wisconsin LLC, we can help you obtain your EIN so it is ready alongside your filed Articles and you can move straight to opening a bank account. We handle the federal application so it matches your Wisconsin formation exactly. The EIN is free from the IRS; where we assist, we are handling the paperwork and coordination, not charging for the number the government provides at no cost.