Insurance Rating Factors: Everything Brokers Need to Know

Insurance rating factors are the variables carriers multiply against a base rate to produce a final premium. For a typical commercial account, 12 to 18 factors interact across the rating sequence. A 5% error on any single factor - a wrong class code, a stale territory assignment, or a missing experience mod - can swing premium by $3,000 to $22,000 on a $150,000 account. Travelers, Hartford, and CNA each apply the same ISO or NCCI filed structure, but their loss cost multipliers differ by 8% to 22%, which is why identical risks generate quotes that vary by 25% to 40% across carriers. Understanding insurance rating factors explained is the foundation of accurate quoting, credible renewal conversations, and substantive client advocacy.

This guide covers two distinct meanings of "rating" that brokers must never conflate, then walks through every rating factor category across four commercial lines.

Key Takeaways

• "Insurance rating" means two unrelated things: carrier financial strength ratings (AM Best) and policy premium rating factors. Confusing them costs credibility with clients.
• Commercial insurance rating follows a fixed sequence: class code, exposure, territory, experience modifier, schedule credits, and program adjustments.
• NCCI publishes approximately 600 workers compensation class codes; ISO publishes over 1,300 general liability classes. A single code error shifts premium by $10,000 to $35,000 on a mid-size account.
• The experience modification factor (mod) is calculated from a 3-year loss history; a mod of 0.85 saves 15% of manual WC premium.
• Schedule rating credits and debits can adjust filed premium by plus or minus 25% within most state filings - but only if you document them before the quote.
• Territory factors range from 0.70 to 2.35 depending on line and geography; commercial auto shows the widest spread.
• Automated submission clearance cuts rating factor errors from 9% to under 2% on new commercial submissions.

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Two Things Called "Rating": A Critical Distinction

Brokers field questions about "insurance ratings" from two completely different contexts. Conflating them with a client or in a submission is a credibility problem.

Carrier financial strength ratings are published by independent credit rating agencies - primarily AM Best, S&P, Fitch, and Moody's. AM Best is the P&C industry standard. The AM Best scale runs from A++ (Superior) at the top through A+, A, A-, B++, B+, B, B- and below. An A- rating or better is required by 87% of commercial lease clauses, most SBA loan covenants, and virtually every certificate holder requirement from a general contractor or municipality.

AM Best's rating reflects the carrier's ability to pay claims, not the price of your client's policy. A carrier rated A by AM Best does not necessarily charge less than one rated B+. These are financial strength indicators, not pricing signals.

Policy premium rating factors are the mathematical inputs that determine your client's actual premium. These are the subject of this guide. They include class codes, territory multipliers, experience modifiers, schedule credits, and exposure bases. None of them appear on the AM Best scale.

When a client asks "what's my insurance rating?" they may mean either. Clarify the question before answering.

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The Four Rating Methodologies

Every commercial premium is built using one or more of four rating methodologies: manual rating, experience rating, schedule rating, and composite rating. Most accounts use all four in sequence.

Manual Rating

Manual rating is the base-level calculation before any account-specific adjustments. It uses:

1. A class code that identifies the operation
2. A filed base rate tied to that class code (expressed per $100 of payroll, per $1,000 of revenue, or per vehicle)
3. A territory factor applied to the base rate
4. An exposure unit (payroll, revenue, square footage, or vehicle count) that sets the premium volume

The carrier's manual rate comes from a loss cost published by ISO or NCCI, multiplied by the carrier's individual loss cost multiplier (LCM). The LCM is carrier-specific and state-filed. A carrier with an LCM of 1.18 on class 5183 (plumbing) will price 18% above the ISO loss cost before any adjustments.

Manual premium = (Exposure / rate unit) x Base rate x Territory factor

For a plumbing contractor with $1.5M payroll in Denver:

• WC class 5183 manual rate (Colorado): $6.40 per $100 payroll
• Territory factor: 1.00 (state-rated, no county modifier on WC)
• Manual premium: ($1,500,000 / 100) x $6.40 = $96,000

Experience Rating

Experience rating applies the experience modification factor (mod or EMR) to manual premium. The mod compares the insured's actual loss history to the expected losses for an average business of the same size and class.

NCCI calculates mods for 38 states. Independent bureaus handle California (WCIRB), New York (NYCIRB), Pennsylvania (PCRB), and seven other states.

Modified premium = Manual premium x Mod

A mod of 0.85 on $96,000 manual = $81,600 modified premium. A mod of 1.30 = $124,800.

The mod uses a 3-year experience period that ends 1 year before the policy effective date. For a policy effective January 1, 2027, the experience period covers January 2023 through December 2025.

Schedule Rating

Schedule rating is an underwriter-applied adjustment to the modified premium. It accounts for account characteristics not captured in the class code or experience period. Categories typically include management quality, premises condition, equipment age, safety programs, and classification peculiarities.

Most state filings allow schedule credits and debits of plus or minus 25% on the combined total. Some states (Indiana, Michigan) allow wider swings.

Scheduled premium = Modified premium x (1 - Schedule credit or + Schedule debit)

Documentation drives the outcome. A 15% schedule credit request with OSHA logs, a written safety manual, and maintenance records earns the credit. The same request with verbal assurances earns 3% to 6%.

Composite Rating

Composite rating applies a single blended rate across multiple exposure types on the same account. A large contractor with payroll, revenue, and vehicle exposures may negotiate a composite rate that simplifies billing and audit. Composite rating is available on accounts above $100,000 in manual premium in most states.

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Class Codes: The Highest-use Factor

The classification code is the single most consequential rating factor. It determines the base rate, and base rate differences across classes span a factor of 14 on workers compensation.

ISO GL Classification

ISO's Commercial Lines Manual contains over 1,300 GL classes. Classes are organized by hazard group (A through F, with F the highest). The base rate per $1,000 of revenue or payroll differs by hazard group.

Source: ISO Commercial Lines Manual, 2025 edition. Rates are illustrative loss costs; actual rates vary by carrier LCM and state filing.

A misclassification between office (41675) and light contracting (97447) on $5M of revenue moves GL premium by $13,350 before territory and experience adjustments.

NCCI WC Class Codes

NCCI publishes approximately 600 workers compensation class codes organized by industry and hazard. The rate differential between the lowest and highest class codes exceeds 14x on identical payroll.

Source: NCCI, 2025 loss costs. Actual rates vary by state and carrier LCM.

Misclassifying 20% of a roofer's payroll ($400,000 of a $2M payroll) as clerical instead of 5551 drops WC manual premium by $73,600 at quote - and generates a $73,600 audit bill at year end.

Verifying Class Codes

Four situations trigger a code review:

1. New account from a different agency (prior broker may have miscoded)
2. Operations description does not match the code on the expiring policy
3. Multiple operations with a single code (split payroll likely needed)
4. Revenue or payroll grew faster than premium - possible exposure understatement

Document the class code justification in the submission narrative. Carriers audit codes during premium audit, and class disputes generate 23% of mid-term premium adjustments per IRMI data.

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Experience Rating Deep Dive

How the Mod Is Calculated

The experience modification formula is:

Mod = (Actual Primary Losses + Weighted Excess Losses + Ballast) / (Expected Primary Losses + Weighted Expected Excess Losses + Ballast)

Primary losses are individual claim amounts below the split point (NCCI split point: $18,500 in 2026). Primary losses are counted at full value in the mod formula.

Excess losses are claim amounts above the split point. Excess losses are weighted by a credibility factor and have less impact on the mod dollar-for-dollar.

Expected losses are the average losses a business of the same payroll, class, and state should produce. They come from NCCI's expected loss rates, which update annually.

Ballast stabilizes the mod for smaller accounts. Larger accounts carry lower ballast and more credibility weight.

Why Frequency Beats Severity in the Mod

Five claims of $12,000 each ($60,000 total) have a larger mod impact than one claim of $60,000.

• Five $12,000 claims: all $60,000 falls in primary (under $18,500 each), fully weighted
• One $60,000 claim: $18,500 primary, $41,500 excess - the $41,500 is heavily discounted

This is the fundamental mod principle brokers must communicate to clients. A sprained wrist that costs $9,000 can move the mod more than a $40,000 surgery if the surgery is the only claim in the period.

Mod Calculation Example

Concrete subcontractor, $2.4M annual payroll, NCCI class 5606, Colorado:

At $0.88, this contractor saves 12% off manual premium, or $23,040 on a $192,000 manual.

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Territory Rating Factors

Territory factors are geographic multipliers applied to the base rate. They reflect ZIP-code or county-level differences in loss frequency, severity, litigation patterns, and catastrophe exposure.

ISO publishes over 1,100 commercial auto territories. Each carrier can file its own territory factors within state-approved ranges. Territory is determined differently by line:

• Workers compensation: State-rated. The mod system absorbs most geographic variation; territory is not a separate factor in most NCCI states.
• General liability: Principal business address or, for products, the distribution territory.
• Commercial auto: Garaging ZIP of each vehicle, not the registration address.
• Commercial property: Building ZIP, protection class, and distance to coast.

Territory Factors by Line - Representative Examples

Source: ISO Commercial Lines Manual, NCCI territory definitions, and carrier filed rating plans. Factors are representative; actual rates vary by carrier and state.

The most common territory error: using the client's billing address instead of the garaging address on commercial auto. A fleet garaged in a suburban ZIP (factor 0.95) billed to a downtown address (factor 1.65) generates an overcharge of $42,000 on a $60,000 fleet premium. For more on verifying and challenging territory assignments, see the full territory rating factors insurance guide.

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Schedule Rating Credits and Debits

Schedule rating is where the underwriter's judgment meets documented evidence. It applies after experience rating and before program credits.

Most ISO-filed schedule rating plans define five credit/debit categories. Maximum credit per category ranges from 5% to 10%, with a combined cap of 25% in most state filings.

Standard Schedule Rating Categories

The underwriter cannot award credit that is not documented. Submit the schedule rating exhibit with the original submission - not after the quote. Pre-submission credit requests succeed 82% of the time. Post-quote requests succeed 34% of the time.

Schedule rating does not apply to workers compensation in most states. NCCI WC plans use experience rating for account-specific adjustments. A few states (Illinois, Minnesota) permit limited schedule modifications on WC.

For the complete documentation workflow, see schedule rating credits and debits.

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General Liability Rating Factors

GL rating factors by the numbers:

Exposure basis: Receipts, payroll, area (square footage), or units - depending on the class. Contractors are rated on payroll or receipts. Retailers on sales. Habitational on units.

Products vs. premises-operations split: Many GL classes carry separate rates for premises-operations (on-site injury) and products-completed operations (post-project injury). A contractor rated on $8M receipts may pay $3.20 per $1,000 on premises-ops and $1.80 per $1,000 on products-completed ops.

Per-occurrence limit loading: Base rates assume $1M per occurrence. Higher limits add a factor. $2M adds approximately 1.10 to 1.14; $5M adds 1.18 to 1.25 depending on class.

GL Rate Example - Concrete Contractor, Chicago:

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Workers Compensation Rating Factors

WC rating is the most formula-driven of the four commercial lines. Every state has a filed rating plan, NCCI or independent bureau, and deviation is limited.

WC rating sequence:

1. Payroll by class code
2. Manual rate per $100 payroll
3. Manual premium
4. Experience mod multiplied against manual premium
5. Premium discount (for larger accounts, applied on a sliding scale)
6. Expense constant (flat dollar amount, typically $200 to $400)
7. State assessment surcharges and taxes

Premium discount is often missed by brokers on growing accounts. Carriers apply a sliding-scale discount to WC accounts above roughly $5,000 in standard premium. At $250,000 standard premium, the discount is approximately 12% to 16% depending on state and carrier.

WC Rating Example - Concrete Subcontractor:

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Commercial Auto Rating Factors

Commercial auto is the most individualized line. Each vehicle is rated separately, and driver history affects every unit in the fleet.

Key rating factors for commercial auto:

• Vehicle type: Light private passenger, medium truck, heavy truck, semi. Rates differ by a factor of 3 to 5 between light and heavy.
• Vehicle use: Service, retail, artisan, or commercial - each carries a different rate multiplier.
• Radius of operation: Local (under 50 miles), intermediate (51 to 200 miles), long-haul (200+). Long-haul adds 35% to 72% to base auto rates.
• Territory (garaging ZIP): Spreads of 3.0x between rural and urban are common.
• Driver MVR: Each driver's motor vehicle record is scored. DUIs add 15% to 40% to vehicle rate; at-fault accidents add 10% to 25%.
• Vehicle age and value: complete and collision rates depend on ACV, which depreciates.

Commercial Auto Rate Example - 8-Unit Fleet, Cleveland:

Driver MVR surcharges added $1,800 on two drivers with recent violations, pushing the final to $30,300.

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Commercial Property Rating Factors

Property rating involves the most carrier-specific variation of the four lines, because catastrophe modeling (for CAT perils) is proprietary to each carrier.

Primary property rating factors:

• Construction class: ISO classifies buildings as Frame (Class 1), Joisted Masonry (2), Non-Combustible (3), Masonry Non-Combustible (4), Modified Fire Resistive (5), and Fire Resistive (6). Frame buildings pay 40% to 80% more than Fire Resistive on identical values.
• Occupancy: Office, retail, manufacturing, restaurant, and habitational each carry different fire hazard ratings.
• Protection class: Based on fire department quality and distance to the nearest station. Protection class 1 (best) to 10. Moving from class 3 to class 9 increases property premium by 30% to 55%.
• Territory and catastrophe exposure: Property in CAT-exposed zones (Florida coastal, Texas Gulf Coast, California wildfire zones) carries surcharges that can double or triple the inland rate.
• Building value: Replacement cost value is the exposure basis. Underinsurance - coverage set below 80% of replacement cost - triggers coinsurance penalties.

Property Territory Examples - Warehouse, $5M Replacement Cost:

The certificate of property insurance for a Miami coastal warehouse must reflect the correct wind coverage limits and deductibles. Missing hurricane deductible language is one of the top 3 certificate errors.

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ISO vs. Proprietary Rates

Not every carrier uses ISO loss costs. Understanding which carriers file independently changes your placement strategy.

ISO-based carriers file their rates as the ISO loss cost multiplied by their LCM. They are transparent and comparable. Hartford, Travelers, CNA, Cincinnati, and most regional carriers file on ISO.

Proprietary rate filers (Zurich, AIG, Chubb for large accounts, and specialty MGA programs) file their own rates with state DOIs. These rates may be higher or lower than ISO depending on the carrier's loss experience and target market. Comparing a proprietary rate to an ISO quote requires converting both to a per-unit basis.

Surplus lines carriers are non-admitted and do not file rates for approval. They can charge any rate the market accepts. Surplus carriers take risks admitted markets decline - typically higher-hazard classes, poor loss histories, and niche operations.

When you receive a surplus lines quote, no rate filing exists to benchmark it against. You evaluate it on coverage terms, carrier AM Best rating (look for A- or better even in surplus lines), and comparative loss cost reasonableness.

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How Underwriters Apply Judgment

Rating plans set the math, but underwriters have discretion within filed guidelines. Three judgment points matter most to brokers:

1. Schedule credit decisions. Within the filed range, the underwriter decides the credit percentage. A well-packaged submission with documentation earns 20% to 25%. A bare application earns 0% to 5%.

2. Deviation filings. Most states allow carriers to file deviation plans that modify individual class rates above or below the filed plan. An underwriter can offer a 10% deviation on a preferred class if the account qualifies.

3. Endorsement and exclusion selection. Underwriters can price out specific exposures with endorsement premiums rather than changing the base rate. A manufacturer with a single high-hazard product line may be rated with the product-line exposure segregated and priced separately.

Brokers who build relationships with underwriters and submit clean, documented accounts get better pricing at all three judgment points. Per IRMI survey data, submissions with complete data packages receive 14% better schedule credits and 18% faster binding decisions than incomplete submissions.

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How Brokers Can Influence Rating Outcomes

Brokers are not passive conduits. Every factor in the rating sequence has a broker intervention point.

Brokers who manage these touchpoints proactively return $15,000 to $90,000 in annual premium savings to middle-market clients on workers compensation alone, per NCCI actuarial benchmarks.

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The Broker Verification Checklist

Before every submission leaves your desk:

1. Class codes match the operations description and payroll split in the application
2. Territory verified against garaging address (auto), operating address (GL), and building address (property)
3. Exposure basis (payroll, revenue, vehicles, square footage) tied to source documents - tax returns, payroll registers, or financial statements
4. Experience mod confirmed from the current NCCI or state bureau worksheet, not last year's
5. Schedule rating exhibit assembled before submission - not after quote
6. Evidence of insurance checked to confirm it reflects the final rated coverage
7. Carrier AM Best rating confirmed at A- or better for standard placements

For the step-by-step rating methodology with actual math for a $185,000 commercial account, see commercial insurance rating methodology. For territory assignment verification, read territory rating factors insurance.

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FAQ

What is the difference between an AM Best carrier rating and a policy rating factor?

An AM Best rating measures the carrier's financial strength and ability to pay claims. It runs from A++ (Superior) to D (Poor). AM Best ratings say nothing about premium price. Policy rating factors - class codes, territory multipliers, experience mods, and schedule credits - are the mathematical inputs that determine what your client pays. A carrier rated A++ by AM Best may quote higher than a carrier rated A- because its loss cost multiplier is larger. Keep the two concepts separate in every client conversation.

How does an experience modification rate affect a workers compensation premium?

The experience mod multiplies directly against manual premium. A mod of 1.00 means average; the insured pays the full manual rate. A mod of 0.85 saves 15% - on a $200,000 manual premium, that is $30,000 returned annually. A mod of 1.25 adds 25%, or $50,000 to the same manual premium. The mod is recalculated each year by NCCI or the applicable state bureau using the insured's actual losses from the prior 3-year period.

What do ISO class codes and NCCI class codes each cover?

ISO class codes apply to general liability (over 1,300 classes), commercial auto, and commercial property. NCCI class codes apply to workers compensation (approximately 600 classes). They are separate systems maintained by separate rating organizations. Most commercial accounts need both: GL class from ISO and WC class from NCCI or the state bureau. A contractor miscoded on either system faces a premium audit adjustment, a mid-term endorsement, or both.

Can schedule rating credits be combined with experience rating?

On general liability and commercial auto, schedule credits typically stack on top of experience rating and apply to the modified premium. On workers compensation, 14 states - including California and New York - prohibit combining schedule credits with experience rating. In those states, the underwriter applies the larger of the two adjustments, not both. Always verify with the state DOI's filed rating plan before promising a client a combined discount.

Which lines of insurance use territory rating factors most aggressively?

Commercial auto shows the widest territory spread - a factor of 3.0x between rural Wyoming and midtown Manhattan on the same vehicle type. Property is a close second, driven by catastrophe exposure in Florida, Texas, and California coastal zones. General liability territory ranges from 0.85 to 1.62 for premises-operations classes. Workers compensation is primarily state-rated; territory within a state is largely absorbed into the class rate and experience mod rather than a separate geographic multiplier.

How do proprietary carrier rates differ from ISO-based rates?

ISO publishes loss costs - the pure risk component of a rate - that any admitted carrier can adopt by filing their own loss cost multiplier with the state DOI. An ISO-based carrier's rate is the loss cost times their LCM. A proprietary rate filer builds their rate from their own loss data and files a complete rate schedule instead of an LCM. Proprietary rates can be higher or lower than ISO, but they are opaque - you cannot benchmark them to a published ISO loss cost. Large-account carriers like Zurich, AIG, and Chubb for complex risks are frequent proprietary filers.

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Written by Javier Sanz, Founder of BrokerageAudit. Last updated April 2026.

Stop submitting incomplete rating data. BrokerageAudit's Submission Intake validates every rating factor - class codes, territory, experience mod, exposure basis, and schedule credits - against source documents before the submission reaches the carrier. Explore Submission Intake →