SIC and NAICS Codes: How the Wrong One Puts You in a High-Risk Bucket

A client came to us after two straight declines on an equipment line his numbers should have qualified for easily. Revenue was solid, time in business was past the two-year mark, personal credit was clean. The equipment-finance underwriter had run his D&B file and flagged the account for manual review — not because of anything he had done, but because his file was still filed under a general contracting code from a subcontracting job he had taken years earlier, before he pivoted the business entirely into commercial cleaning. On paper, an underwriter's risk model saw a construction company. Construction skews toward higher failure rates and heavier collateral risk than commercial cleaning, so the file got treated accordingly.

Nobody had lied about anything. Nobody had done anything fraudulent. A code nobody had ever revisited was doing quiet, compounding damage to every financing conversation for years.

Two different codes, two different jobs

SIC (Standard Industrial Classification) is a four-digit federal classification system built in the 1930s. The government stopped actively maintaining it decades ago, but it never disappeared — Dun & Bradstreet and a number of commercial credit bureaus, insurers, and legacy underwriting systems still key their models to it, in part because so much historical data is coded to it.

NAICS (North American Industry Classification System) is the current federal standard, jointly maintained by the U.S., Canada, and Mexico, and it is what the SBA's own Table of Small Business Size Standards is matched to. Every SBA loan program eligibility check, and a growing share of modern commercial underwriting, runs off a six-digit NAICS code, not the older SIC number.

Most businesses are filed under both, at different bureaus and different agencies, and the two codes are not always in sync with each other or with what the business actually does today. That gap is where the damage happens.

Why the SBA angle matters: size standards are set per code, not per business

The SBA does not apply one universal definition of "small business." It sets a distinct size standard — either a dollar cap on average annual receipts or a cap on number of employees — for every individual six-digit NAICS code, published in the SBA's own size-standards table and codified at 13 CFR Part 121. Pulled directly from that table, the spread inside a single sector is wider than most owners assume: within Accommodation and Food Services alone, closely adjacent NAICS codes carry receipts-based size standards ranging from $8.0 million up to $41.5 million in average annual receipts — a more than fivefold difference between codes that, from the outside, look like variations on the same business.

How much a size standard can swing inside one sector

Six closely adjacent food-service NAICS codes in the SBA's own table span more than a 5x range in the receipts cap that defines “small.”

Employee-based standards vary just as widely: several 336-series aircraft, aircraft-engine and guided-missile/space-vehicle manufacturing NAICS codes use a 1,500-employee standard, among the highest in the table. The point is the same either way — there is no single “small business” threshold; it is set per 6-digit NAICS code, and picking the wrong code can silently swap which number applies to you.

View the data as a table

	Value
Lowest observed in Accommodation & Food Services	$8.0M avg. annual receipts
Highest observed in the same sector	$41.5M avg. annual receipts

Employee-based standards swing just as hard. Several 336-series NAICS codes — aircraft manufacturing, aircraft engine and engine parts manufacturing, and guided missile and space vehicle manufacturing — use a size standard of 1,500 employees, among the highest employee caps in the entire table, while many services and retail codes cap out in the low hundreds.

There is no single "small business" line. It is set per six-digit code, and the code attached to your file — correct or not — decides which line applies to you.

File your business under the wrong NAICS code and one of two things happens on an SBA application: you either look larger than your actual size standard allows (jeopardizing SBA eligibility on a technicality that has nothing to do with your real revenue), or you look smaller than the code your real activity would carry, and a lender's own internal risk model treats you more cautiously than your actual industry track record justifies.

Why the SIC/high-risk angle matters: bureaus and underwriters bucket by code

Separately from SBA eligibility, commercial credit bureaus and merchant/lender underwriting systems use SIC and NAICS codes as one input into industry-risk classification. Dun & Bradstreet's own explainer on the topic confirms both code systems remain in active use across its products and describes them as central to how a business's industry gets classified for credit and marketing purposes. Neither D&B nor Experian publishes a public list of specific codes scored as "high risk" with disclosed weights — that part of the model is proprietary — but the mechanism is well documented: a business is filed under a code, that code carries an implicit or explicit industry-failure-rate and volatility profile, and the file inherits it.

In practice, the industries that repeatedly show up flagged this way share common traits: high historical failure rates, cash-intensive operations that are hard to verify, heavy regulatory exposure, or revenue that swings hard with economic cycles. Restaurants, general construction and subcontracting, used-vehicle sales, and certain personal services have all been cited by commercial-credit practitioners as categories that draw extra underwriting scrutiny under some bureaus' models — not because every business in those categories is actually risky, but because the code itself carries the reputation of the category.

How a wrong code actually gets attached

• The entity was formed for one purpose and pivoted. Our client's file is the common version — a business starts in one line of work, the code gets set once at formation or first bureau contact, and the business evolves for years while the code never does.
• A generic or "closest match" code was picked at registration. State registration forms, EIN applications, and initial bank or bureau onboarding often ask for a code with limited guidance, and a generic catch-all gets selected because nothing more specific was obvious at the time.
• Different agencies and bureaus never sync. The code on file with your state, your bank, D&B, Experian Business, and the IRS can all differ, because nothing forces them to reconcile with each other automatically.
• A broker or lender misclassified the deal. Occasionally the wrong code enters a file not through the business's own action, but through a lender or platform coding an application incorrectly on intake.

How to check and correct your codes

1. Pull your own D&B and Experian Business files and look at the industry classification each one lists — not just the summary description, the actual SIC and NAICS codes on file. Related reading: our guide to credit monitoring for LLCs covers how to pull and read these files on an ongoing basis.
2. Compare both codes to what the business genuinely does today, not what it did at formation. If the business has meaningfully changed its primary activity, the code should reflect current reality.
3. Check your NAICS code against your entity's IRS and state filings as well — those often carry the code used to determine SBA size-standard eligibility if you ever apply.
4. Contact the bureau directly to request an update. D&B and Experian Business both accept requests to review and correct a listed industry code; be specific about the current primary NAICS code and be prepared to describe actual revenue by activity if the business operates in more than one line of work.
5. Re-pull your file after the correction posts to confirm the update took, the same way you would verify any other change to your business credit file — see our notes on how reporting changes actually post to a file before assuming a request was processed.

This is worth doing before you apply for financing, not after a decline forces the question. A lender's underwriting read of "what kind of business is this" is formed the moment your file is pulled — before a human ever reads your revenue numbers — and the code sets that first impression. We check the classification codes on file at every bureau as part of the same review our business lending advocacy runs before recommending which program to apply to, precisely because a stale code has cost real applicants real approvals. If you have never checked yours, start with the fundability checklist or schedule a consultation before your next application.

Important: MidBank is not a bank, a financial institution, or a financial advisor. We are an advocate and ISO affiliate that connects businesses to vetted third-party providers. This article is general information published on August 18, 2026, not legal, tax, or financial advice — rules and rates change, and your situation is specific to you. Confirm details with the primary sources linked above and with a qualified tax or legal professional before acting.