To change your NAICS code with the IRS, enter the correct six-digit code on your next annual business tax return. The IRS updates its records from the most recently processed return, so no separate form, letter, or standalone request is required in ordinary circumstances. There is no dedicated IRS procedure for a NAICS code correction outside the return itself.
Where the Code Goes on Each Return
The line varies by entity type, but the principle is the same: put the corrected six-digit code where the form asks for your principal business activity code, and the IRS’s records follow.
Schedule C (Sole Proprietors and Single-Member LLCs)
Enter the six-digit code on Line B of Schedule C, filed with your Form 1040. The Schedule C instructions include the full list of codes at the back and direct you to pick the category that best describes your primary business activity. Single-member LLCs that haven’t elected corporate treatment file on Schedule C as well.1Internal Revenue Service. 2025 Instructions for Schedule C (Form 1040) – Profit or Loss From Business
Form 1120 (C Corporations)
C corporations enter the business activity code on page 1 of Form 1120. The list of principal business activity codes appears near the back of the form’s instructions.2Internal Revenue Service. About Form 1120, U.S. Corporation Income Tax Return
Form 1120-S (S Corporations)
S corporations enter the code on page 1, Item B. The instructions tell you to determine which activity produces the largest percentage of total receipts, defined as gross receipts plus all other income including amounts on Schedule K and Form 8825, and use that activity’s six-digit code.3Internal Revenue Service. 2025 Instructions for Form 1120-S – U.S. Income Tax Return for an S Corporation
Form 1065 (Partnerships)
Partnerships enter the six-digit code in Item C on page 1 of Form 1065. The same largest-share-of-receipts rule applies when the partnership has multiple lines of business.4Internal Revenue Service. 2025 Instructions for Form 1065
Form 990 (Tax-Exempt Organizations)
Tax-exempt organizations that report program service revenue or other revenue in Part VIII of Form 990 enter a business activity code alongside the revenue lines (2a through 2e and 11a through 11c), drawn from the NAICS-based list in the Form 990 instructions.5Internal Revenue Service. 2025 Instructions for Form 990 Return of Organization Exempt From Income Tax
Form 5500 (Employee Benefit Plans)
If your business sponsors an employee benefit plan, the six-digit principal business activity code also appears on Form 5500, Part II, line 2d. To correct a previously filed Form 5500, you must submit a complete amended return; you cannot amend the code field on its own.6Department of Labor. 2025 Instructions for Form 5500 Annual Return/Report of Employee Benefit Plan
Can You Change the Code Without Filing a Return?
This is where the advice online gets thinner than it looks. Some guides suggest mailing the IRS service center a letter with your EIN, the old code, the new code, and an explanation. The IRS does not publish a formal procedure for that. Form 8822-B, which businesses use to notify the IRS of changes, covers only address updates and responsible party changes, not business activity codes. There is no dedicated IRS form for a standalone NAICS code correction.
The reliable path is the next return. If your filing date is months away and you’re worried about the mismatch in the meantime, the practical risk is low: the NAICS code is a classification field, not a tax-liability field. If you have a specific reason you need the change reflected sooner, such as an SBA loan application that depends on the code the IRS has on file, call the IRS Business and Specialty Tax Line rather than mailing an unsolicited letter.
Picking the Right Code Before You File
The Census Bureau maintains the official NAICS structure, and the six-digit code is the most specific level.7U.S. Census Bureau. North American Industry Classification System – NAICS Start at census.gov/naics and work down from the broad sector to your specific activity.
The rule for choosing when your business does more than one thing: pick the activity that generates the largest share of your total revenue. A firm doing 60 percent web design and 40 percent digital marketing uses the web design code. The IRS instructions for each business form say the same thing, directing you to the code matching the activity that produces the largest percentage of total receipts.3Internal Revenue Service. 2025 Instructions for Form 1120-S – U.S. Income Tax Return for an S Corporation
The most common reasons a code needs changing are simple. The business pivoted, so the code no longer describes where the money comes from. Or the original code was a rough guess made during setup and was never right to begin with. Occasionally the IRS itself sends a letter noting that your current code doesn’t match the financial data on your returns; the cleanest response is to correct the code on your next filing.
Is There a Penalty for the Wrong Code?
No. IRS penalties apply to failure to file, underreporting income, and missed payment deadlines, among other compliance failures.8Internal Revenue Service. Penalties An incorrect NAICS code doesn’t fit any of those. It’s a classification tool, not a tax-computation input, and it doesn’t change what you owe.
No penalty is not the same as no consequences. A mismatched code can skew how your return compares to industry norms and affect your Discriminant Information Function (DIF) audit score, since the IRS establishes DIF cutoff scores broken down by activity code and pulls the highest-scored returns in each category for examination.9Internal Revenue Service. Workload Identification and Survey Procedures It can also affect SBA eligibility, because SBA size standards are set separately for each NAICS industry, some measured in annual revenue and some in employee count. A general freight trucking company qualifies as small up to $43 million in receipts; a soybean farm hits the ceiling at $2.25 million. Contracting officers assign a NAICS code to each solicitation, and your business must fall below that code’s size standard to bid as a small business concern.10eCFR. Part 121 Small Business Size Regulations The wrong code won’t cost you a fine, but it can quietly cost you eligibility or invite scrutiny that a correct code would have avoided.