EIN Guide for Your Arizona Corporation

An Employer Identification Number (EIN) is a nine-digit federal tax ID issued by the IRS, formatted as XX-XXXXXXX. It's the business equivalent of a Social Security number — the number that identifies your corporation to the federal government for tax purposes.

Corporations always need one

Unlike a single-member LLC, which can sometimes get by on the owner's Social Security number, a corporation always needs its own EIN. That's because a corporation is a separate taxpayer: a C-corporation files its own return (Form 1120) and an S-corporation files Form 1120-S, and neither can be filed under an individual's SSN. The moment you incorporate, an EIN is on the required list.

What you'll use it for

• Filing the corporation's federal tax returns
• Opening a corporate bank account (banks require it)
• Hiring employees and handling payroll tax withholding
• Filing the S-corporation election (Form 2553), which asks for the EIN
• Registering for Arizona transaction privilege tax and setting up state accounts
• Applying for business licenses and, often, opening merchant or credit accounts

In short, the EIN is the first thing you need after the corporation is chartered, before you can really do anything operational.

The most important thing to know about the EIN is that it is completely free from the IRS. There is no government fee. If a service offers to "get your EIN" for a charge, you're paying for their time to complete a short form you can do yourself.

The online application

Apply through the IRS EIN Assistant at IRS.gov. The online tool is the fastest route:

1. Confirm the corporation is already formed (apply after the ACC approves your Articles, so the legal name and structure are settled).
2. Select "corporation" as the entity type.
3. Provide the corporation's legal name, Arizona address, and formation details.
4. Name the responsible party — the individual who ultimately controls the corporation — along with their SSN or ITIN.
5. Answer questions about employees and your expected activities.
6. Submit, and the EIN is issued immediately. Download and save the confirmation (the CP 575 notice or the online summary).

The whole process takes about ten minutes, and you can use the number the same day to open a bank account or file elections.

Hours and one-per-day rule

The online EIN Assistant operates during set hours (generally weekdays, not around the clock) and limits you to one EIN per responsible party per day. Plan to complete the session in one sitting, since it times out after a period of inactivity.

Because Arizona has no residency requirement, plenty of Arizona corporations have owners who aren't US persons. You can still get an EIN — the online tool just isn't available to you.

Form SS-4 by fax or mail

If the responsible party doesn't have an SSN or ITIN, you apply using Form SS-4, submitted by fax or mail to the IRS. Fax is faster than mail; the IRS returns the assigned EIN on the SS-4 or by separate notice. International applicants can also apply by phone through the IRS's international line in some cases. Because these routes take longer than the instant online tool, start early if a non-US responsible party is involved and you have a deadline like opening a bank account.

The responsible party

The IRS requires a real human being as the responsible party — the person who ultimately owns or controls the corporation — not another entity (with narrow exceptions). Choose the right person up front, because changing the responsible party later requires a separate filing (Form 8822-B).

The EIN is federal, but it's the key that unlocks your Arizona state tax setup, so it's worth understanding how the pieces connect.

Transaction privilege tax (TPT)

If your corporation sells taxable goods (and many services), you register for Arizona's transaction privilege tax with the Arizona Department of Revenue, and you'll use your EIN to do it. TPT is Arizona's version of a sales tax, though it's technically a tax on the privilege of doing business. Registration and filing frequency depend on your activity.

Corporate income tax and withholding

Your EIN identifies the corporation on its Arizona corporate income tax filings and, if you have employees, on Arizona withholding accounts for payroll. Setting up these accounts with the Department of Revenue is a separate step from getting the EIN, but the EIN is what ties them all to your corporation.

Keep the confirmation safe

Store the IRS confirmation notice with your corporate records. Banks, the state, lenders, and payroll providers will all ask for the EIN, and having the official confirmation on hand avoids repeated calls to the IRS to retrieve it.

A few missteps around the EIN cause avoidable friction for new Arizona corporations.

Applying before the corporation is formed. Get the EIN after the ACC approves your Articles, so the legal name and structure on the EIN match the state record. An EIN tied to a name that doesn't match your Articles causes headaches at the bank.

Paying for it. As above, the EIN is free. Don't pay a standalone markup for a ten-minute form.

Using a personal SSN instead. A corporation can't run on the owner's SSN the way a sole proprietor can. Get the corporation its own EIN so business and personal tax identities stay separate — which also protects the liability shield.

Losing the confirmation. If you misplace the EIN, you can retrieve it by calling the IRS Business & Specialty Tax Line, but it's far easier to save the confirmation notice from the start.

Picking the wrong responsible party. Name the person who truly controls the corporation. Correcting it later means filing Form 8822-B, so get it right the first time.