EIN Guide for a New Mexico Corporation

An Employer Identification Number is a nine-digit federal tax identifier issued by the IRS, written in the format 12-3456789. Think of it as the corporation's equivalent of a Social Security number — a unique ID that the IRS, banks, and other institutions use to identify the business.

Why every corporation needs one

A corporation is a separate taxpayer from its owners, so it always needs its own EIN — this is different from a single-member LLC, which can sometimes use the owner's Social Security number. Whether your New Mexico corporation is taxed as a C corporation or has elected S status, it needs an EIN because:

• It files its own tax return. A C corporation files Form 1120; an S corporation files Form 1120-S. Both require an EIN.
• Banks require it. No bank will open a corporate account without the EIN.
• Payroll requires it. If the corporation has employees — and in an S corporation, owner-employees typically take a salary — you need an EIN to handle payroll tax deposits and filings.
• Vendors and clients may request it. It appears on forms like the W-9 when the corporation is paid.

There is no scenario where a functioning corporation gets by without an EIN, which is why obtaining it is a standard early step right after formation.

Apply for the EIN after your Articles of Incorporation are filed and the corporation legally exists, but before you try to open a bank account or run payroll. The sequence matters because the IRS asks for the corporation's legal name and formation details, which should match what New Mexico has on record.

The right order

1. File the Articles of Incorporation with the New Mexico Secretary of State and let the state record them.
2. Apply for the EIN once the corporation exists.
3. Use the EIN to open the corporate bank account, register for state taxes, and set up payroll.

Applying before the corporation is formed risks a mismatch between the name on the EIN and the name on the state record, which causes headaches at the bank. Wait until the entity is on the books, then apply.

The IRS offers several ways to apply, and it never charges a fee. If a website offers to get you an EIN for a price, you are paying for someone to fill out a free government form on your behalf.

Apply online (fastest)

The online application through the IRS EIN Assistant is the fastest route. It takes about ten minutes, and the EIN is issued immediately at the end — you can download the confirmation and use the number the same day. The online tool is available during set hours and must be completed in one session; it does not save partway through. To apply online, the responsible party must have a US Social Security number or ITIN.

Apply by fax or mail

If you cannot apply online — most commonly because the responsible party has no SSN or ITIN — you complete IRS Form SS-4 and submit it by fax or mail. Fax responses typically come back within a few business days; mail takes several weeks. This is the standard path for many international founders.

What information you will need

• The corporation's exact legal name as filed with New Mexico
• The state and date of incorporation
• The corporation's mailing address
• The name and taxpayer ID of the responsible party
• The reason for applying (started a new business) and the type of entity (corporation)

Every EIN application requires a "responsible party" — and this is where applicants most often get confused, so it is worth understanding clearly.

Who the responsible party is

The IRS defines the responsible party as the individual who ultimately owns or controls the corporation, or who exercises effective control over it. For a corporation, this is usually a principal officer or a controlling shareholder. It must be a natural person — not another company — except in limited government cases. The responsible party provides their own name and Social Security number or ITIN on the application.

Why it matters

The responsible party is the human the IRS associates with the corporation's tax matters. If control of the corporation changes hands later, the IRS expects you to update the responsible party using Form 8822-B. Naming the right person up front, and keeping it current, avoids confusion if the IRS ever needs to reach the person truly in charge.

One responsible party, real control

Do not name a passive investor or someone with a title but no actual authority just to fill the field. The point of the responsible-party rule is to identify who genuinely controls the corporation. Pick the person who fits that description.

New Mexico's privacy-friendly reputation attracts international founders, and a common question is how to get an EIN with no US Social Security number. It is entirely possible — the online tool is simply not the route.

The path for non-US responsible parties

If the responsible party has neither an SSN nor an ITIN, you cannot use the instant online application. Instead:

• Complete Form SS-4 by hand, entering "Foreign" in the space for the responsible party's SSN/ITIN where instructed.
• Submit the form to the IRS by fax or mail.
• Expect the EIN back by fax in roughly a few business days, or by mail in several weeks.

The corporation still gets a valid EIN this way — it just takes longer than the online path. You do not need to obtain an ITIN first solely to get the EIN; the "Foreign" entry on Form SS-4 handles the situation. Many international owners of New Mexico corporations use exactly this process to get their federal tax ID and then open a US bank account.

After you have the EIN

Once the EIN is issued, keep the confirmation somewhere safe — banks and the IRS will ask for it repeatedly. Use it to open the corporate bank account, register with the New Mexico Taxation and Revenue Department for gross receipts tax if you sell taxable goods or services, and set up payroll if the corporation has employees. Mainstay Filing focuses on the state formation and registered agent side; the EIN itself is free and straightforward to obtain directly from the IRS using the steps above.