To find out how the IRS classifies your business, look at three things in this order: the form number on your most recently filed business tax return, the paperwork you received when you got your EIN, and, if those don’t answer it, the IRS itself by phone or through your online business account. Knowing how to know your tax classification comes down to matching those records against the four categories the IRS uses — sole proprietorship, partnership, C corporation, or S corporation — plus the disregarded-entity treatment applied to most single-member LLCs.
Start With the Return You Last Filed
The return your business filed last year is the clearest evidence of how the IRS currently treats it. The form number on the first page tells you the classification without any interpretation needed.
- Schedule C attached to your personal Form 1040 means you’re filing as a sole proprietorship, or as a single-member LLC treated as a disregarded entity. A single-member LLC files Schedule C unless it has elected corporate treatment.1Internal Revenue Service. 2025 Instructions for Schedule C (Form 1040) – Profit or Loss From Business
- Form 1065 means you’re filing as a partnership. The business files an informational return and issues each partner a Schedule K-1.2Internal Revenue Service. About Form 1065, U.S. Return of Partnership Income
- Form 1120 means you’re filing as a C corporation, with the entity itself paying tax on its income.3Internal Revenue Service. Form 1120 U.S. Corporation Income Tax Return
- Form 1120-S means you’re filing as an S corporation. The business reports income on this return, but profits pass through to shareholders on their personal returns.4Internal Revenue Service. About Form 1120-S, U.S. Income Tax Return for an S Corporation
If the form your accountant filed doesn’t match what you expected based on how you set the business up, treat that as a signal to keep digging. It can mean an election was never processed, or that a return was filed under the wrong status.
Check Your Formation and Election Documents
If you haven’t filed a return yet, or you want to confirm what should have been filed, pull the paperwork from when you first set up the business with the IRS.
Form SS-4 and the CP 575 Notice
When you applied for your Employer Identification Number, Form SS-4 asked you to identify the entity type on line 9a — sole proprietor, corporation, partnership, or other. That selection established your business tax account.5Internal Revenue Service. Instructions for Form SS-4 (12/2025) After processing the SS-4, the IRS mailed a CP 575 notice confirming the EIN assignment. Online applicants may have received the notice as a downloadable document at the time of application.6Internal Revenue Service. Employer Identification Number Between the two, you can see what classification you originally told the IRS you were.
Form 8832 (Entity Classification Election)
If your business chose a classification different from its default — an LLC electing corporate treatment, for example — you would have filed Form 8832. A copy in your records shows both the elected classification and its effective date.7Internal Revenue Service. Form 8832 Entity Classification Election
Form 2553 (S Corporation Election)
An S corporation election is made on Form 2553 under Section 1362(a).8Internal Revenue Service. About Form 2553, Election by a Small Business Corporation The IRS sends a confirmation letter when it accepts the election, so look for that letter alongside your filed copy. If you can’t find either, the election may never have been processed, and your business may still be classified as whatever it was before.
Ask the IRS Directly
When your own records are incomplete or contradict each other, go to the source.
Call the Business and Specialty Tax Line
You can reach the IRS at 800-829-4933, Monday through Friday, 7 a.m. to 7 p.m. in your local time zone.9Internal Revenue Service. Telephone Assistance Contacts for Business Customers An authorized person — usually an owner, officer, or someone listed on the SS-4 — must give the entity’s full legal name, business address, and EIN. The representative can verbally confirm how the IRS currently classifies your entity.
On the same call, ask for a 147C letter. It’s written confirmation of your EIN and the business name on file, and it’s what banks and vendors ask for when they need proof of your business identity.6Internal Revenue Service. Employer Identification Number
Use Your Online Business Tax Account
The IRS Business Tax Account lets you view your business profile, account balance, tax records, and notices online.10Internal Revenue Service. Business Tax Account Sole proprietors and designated officials of corporations can access it after identity verification. The account may not print a line reading “tax classification,” but your business profile and tax transcripts will show which return types the IRS associates with your EIN, which answers the same question.
Send an Accountant or Attorney on Your Behalf
If you’d rather have a professional handle the call, they’ll need a signed Form 2848 (Power of Attorney and Declaration of Representative) to access your confidential tax information.11Internal Revenue Service. Instructions for Form 2848 Power of Attorney and Declaration of Representative The representative has to be someone eligible to practice before the IRS, such as a licensed attorney, CPA, or enrolled agent.
Your Default Classification If You Never Elected
If you never filed Form 8832 or Form 2553, the IRS classified your business automatically based on how you organized it under state law. These defaults come from Treasury Regulation Section 301.7701-3.12eCFR. 26 CFR 301.7701-3 – Classification of Certain Business Entities
- A sole proprietor — someone running a business alone without incorporating — is treated by the IRS as one taxable unit with the individual.
- A single-member LLC is a disregarded entity by default. The owner reports the LLC’s income on a personal return, the same way a sole proprietor does.
- An LLC with two or more members is a partnership by default. The business files its own informational return, and income passes through to each owner.
- A business that incorporates under state law is a C corporation by default, and the entity itself pays income tax on its profits.
If your formation type points to one of these defaults and you can’t find a Form 8832 or 2553 in your records, that default is almost certainly what the IRS has on file for you.
Why Getting This Right Matters
Filing under the wrong classification — or under one the IRS doesn’t have on record for you — creates real financial exposure. An underpayment tied to the wrong return can draw an accuracy-related penalty of 20% of the underpayment, with interest accruing until the balance is paid.13Internal Revenue Service. Accuracy-Related Penalty A business that should be filing as a partnership or S corporation but isn’t can owe a per-owner, per-month failure-to-file penalty; for returns due in 2026, that runs $255 per partner or shareholder each month, for up to 12 months.14Internal Revenue Service. 20.1.2 Failure to File/Failure to Pay Penalties And the standard three-year audit window stretches to six years when more than 25% of gross income is omitted, with no time limit at all when a return is found to be fraudulent.15Internal Revenue Service. Overview of Statute of Limitations on the Assessment of Tax
If your records and the IRS’s records don’t line up, the fix is to reconcile them before the next return is filed, not after. Start with your last filed return, work back through your formation and election paperwork, and confirm with the IRS if anything still doesn’t match.