General Liability Class Codes: How They Work and How Agents Choose One
A general liability class code places an insured's operations into one classification from ISO's general liability system. Each classification has a premium basis, such as gross sales, payroll, area or units, and the carrier applies that class's rate to the insured's estimated exposure in that basis. The class therefore decides what gets measured and what rate applies. Pick it from a current source, and confirm it with each carrier.
For a quick lookup of common codes, use the class code lookup tool. For a short definition, see the general liability class code glossary entry. This guide covers what the glossary does not: how the premium basis works, how the system has changed, and a repeatable way to choose and check a class on a submission.
What a GL class code does
Three things happen once an operation is assigned to a class.
The class sets the rate. ISO, the Insurance Services Office, is the organization behind the general liability classification system and loss cost data (ISO glossary entry). Verisk, which publishes the ISO program, says that assigning risks to their correct classification helps ensure an insurer charges adequate premiums and understands the risk it is adding (Verisk, September 2021).
The class sets the premium basis. Each classification names the unit the exposure is counted in. That unit is what the insured estimates on the application and what an auditor checks after the policy year.
The class shapes appetite. Carriers decide which operations they want to write, and the class is how an underwriter reads the operation at a glance. A submission under the wrong class can be declined for an operation the insured does not perform, or quoted on the wrong assumptions. See carrier appetite and the appetite checker.
Premium basis: the unit the class is measured in
Westfield Insurance's premium audit guide defines the GL rating bases an auditor uses (Westfield Premium Audit Reference Guide). In its words, restated here:
| Premium basis | What it counts (per Westfield) | Where it typically applies |
|---|---|---|
| Gross sales | Amounts charged for goods sold or distributed, services performed during the policy period, rentals, dues and fees | Westfield calls it the most common basis for non-construction businesses |
| Gross payroll | Wages, salaries, bonuses, holiday pay and vacation pay | Westfield says construction companies are typically rated on it |
| Total cost | Cost of all work let or sublet for a project, including labor, materials and equipment | Westfield pairs it with construction firms that use subcontractors |
| Each (units) | Units of exposure, with the unit size set in the classification footnotes, such as per person | Classes measured per item or per person |
| Admissions | People admitted to events on the premises, including paid, ticketed and complimentary entries | Classes measured by attendance |
Verisk gives payroll and the square footage of commercial office space as examples of exposure units, and says payroll is the ISO general liability premium base for most contracting and service risks (Verisk, September 2021).
The arithmetic is the same whatever the basis: exposure, divided by the unit size, times the class rate, then adjusted by the carrier's own modifiers and schedule credits or debits (schedule credits and debits). As a made-up illustration, not a real rate: an insured with 2,000,000 in estimated gross sales on a class rated at 2.00 per 1,000 of sales would produce 4,000 of premium before modifiers. Real rates vary by carrier, state and class.
Why the basis matters at audit
The exposure on the application is an estimate. After the policy year, the carrier checks it against records. Westfield lists the records its auditors ask for on the sales side (profit and loss statement, income statement, sales journals, general ledger) and on the payroll side (payroll journals and registers). Westfield says an audit ends in either a bill for additional premium or a refund, so a low estimate tends to come back as a bill. See premium audit, revenue-based rating and payroll-based rating.
Subcontractors change which class and basis apply
For contractors, who performs the work matters as much as what the work is. Westfield's guide says work done by an adequately insured subcontractor is assigned to the appropriate "contractors-subcontracted work" classification, while work by a subcontractor without adequate insurance is classified and rated under the class for the operation itself. Westfield defines an adequately insured subcontractor as one that carries limits at least equal to the policy's limits or at least $1,000,000 per occurrence, holds comparable coverages, and provides evidence of insurance. Those thresholds are Westfield's; other carriers set their own. The practical point for agents is to collect subcontractor certificates at submission, not at audit. See how to quote contractors.
The system changes, so code lists age
Verisk announced a major revision to the ISO general liability classification system in 2021. Its September 2021 post lists:
- 58 entirely new classifications
- 249 classes discontinued
- premium base changes to 17 classes
- 214 class revisions with potential rating impact
- 20 existing classes split into 40
- 136 classes streamlined into 61
A second Verisk post from the same period gives a different headline figure, 70 new classes, and says it planned to begin filing the program in the second quarter of 2021 with an effective date about 18 months after filing (Verisk, sweeping enhancements). The two posts count differently, so we cite both and do not reconcile them. The takeaway is the same: filings and effective dates are state and carrier specific, so a class code copied from an older blog post or an old application may no longer be the class a carrier uses today. Verisk also says the new class sections show the premium base, how the class should be applied, mandatory endorsements and which parts of the risk need separate classification.
That is the reason this guide does not print a table of "top codes by trade." We did not fetch a primary ISO or carrier code list for this guide, and an unsourced list is exactly the kind of thing that goes stale. Use the class code lookup for the common codes it shows, and confirm the final class in the carrier's current rating guide or with its underwriter. Verisk's premium audit service also offers classification guides with descriptions of ISO GL classes and guidance on applying them (Verisk premium audit advisory service).
How agents choose and check a class
- Write the operations in plain words first. Include what the insured sells, installs, repairs or hosts, and what it subcontracts. The ACORD 125 operations description and the ACORD 126 classification section both ask for it.
- Find the candidate class. Start with the class code lookup for a likely code, then confirm against the carrier's rating guide. Do not rely on the business name; rely on the work.
- Read the premium basis for that class. Confirm whether the carrier measures sales, payroll, area, units or total cost, and whether the carrier's form asks for the right number.
- Collect the exposure number from records. Ask for projected sales or payroll for the coming term and compare it with last year's tax return or financials. The same logic appears in what you need for a business insurance quote.
- Split or combine deliberately. If an insured has distinct operations, ask the carrier whether it wants them rated as one class or several. Do not decide alone. The general liability class code glossary entry and risk classification explain the idea.
- Re-check with every carrier. Different carriers can read the same operation differently. Before you compare prices, make sure each quote is built on the same class and basis, or the comparison is not like for like.
- Keep the file consistent. The class on the 126 should match the description on the 125, the carrier portal entries and any supplemental application. A mismatch is the first thing an underwriter asks about. The submission checklist covers the rest of the package.
Common ways a class goes wrong
- Class chosen from the business name. A shop called "Smith Plumbing and Supply" may sell more than it installs. The work, not the name, drives the class.
- Right class, wrong exposure. A low sales or payroll estimate keeps the quote cheap, then returns as additional premium at audit.
- Subcontractors left out. Uninsured subcontractor work is rated under the class for the operation itself, per Westfield, which can move a job into a higher-rated class.
- Mixed operations forced into one code. If a business does two distinct things, a single code can understate one of them.
- Using the WC code for GL, or the reverse. The two systems classify differently and use different bases. See NCCI class codes, NAICS codes and how to quote workers' comp.
- Carried-over codes. A renewal application with last year's class is not proof that the class is still the one the carrier uses.
FAQ
What is a general liability class code?
It is a number from ISO's general liability classification system that assigns an insured's operations to a class. The class sets the premium basis and links the operation to a rate. Codes are five digits in the ISO system.
Does the class code or the revenue set the premium?
Both. The class decides which rate and which basis apply. The exposure, such as sales or payroll, is what that rate is multiplied by. A correct class with an understated exposure still produces the wrong premium.
What is the difference between a GL class code and a NAICS code?
NAICS describes an industry, while a GL class code is a rating classification. Applications often ask for both, so treat NAICS as its own field and not a substitute for the class. See NAICS codes in insurance.
Can a business have more than one GL class?
Yes. An insured with distinct operations may be rated under several classes, each with its own exposure. Ask the carrier how it wants mixed operations presented.
Where can I look up a GL class code?
Start with the class code lookup, which lists common codes by type of business. Confirm the final class in the carrier's current rating guide, or with its underwriter, because carriers and states adopt ISO class revisions on their own schedules.
What we checked and what we did not
Checked 7 November 2026: the two Verisk posts and the Verisk premium audit page (fetched), and Westfield Insurance's Premium Audit Reference Guide (fetched, undated, copyright 2024). Not verified: the ISO Commercial Lines Manual itself, which we did not obtain, any specific class code or rate, and which ISO classification edition each carrier or state uses today. The five-digit format of ISO GL codes is consistent with ISO's statistical reporting practice (for example, the Texas Department of Insurance commercial lines statistical plan names ISO as statistical agent and carries a five-position numeric classification field) but we did not confirm it against the manual.
