California Workers’ Compensation Rates: Formula, Discounts, and Audits

California workers’ compensation rates currently average $1.52 per $100 of payroll as an approved advisory pure premium rate, effective September 1, 2025.¹ That statewide average is only a benchmark. What you actually pay turns on three things: the classification code assigned to your work, your own claims history expressed as an experience modification factor, and the insurer you buy from. A roofing contractor and an accounting firm start from radically different base rates, and two insurers quoting the same business can land in different places.

The Formula Behind Every Premium

Every California workers’ compensation premium is built the same way. Take your classification rate per $100 of payroll, multiply by your experience modification factor, then multiply by your total payroll divided by 100.

A worked example: a classification rate of $2.50, an experience modification of 0.90, and annual payroll of $500,000 produces a base premium of $2.50 × 0.90 × 5,000, or $11,250. The insurer then layers its own expense loading on top of that figure, and the state adds a mandatory assessment. The final bill is higher than the base.

Each piece of the formula behaves differently. Your classification is largely fixed by the nature of what you do. Your experience modification moves year to year with your claims. Your payroll moves with your business. And the insurer’s markup is the one piece that competition can discipline, because carriers set their own final prices around the regulatory baseline.

How Industry Classification Sets Your Base Rate

California’s rating system includes roughly 700 industry classifications, each grouping employers whose operations carry similar injury risk.² A staffing agency, a restaurant, and a tree-trimming crew face different hazards, and each carries a different rate per $100 of payroll.

The spread between the safest and riskiest codes is dramatic. Clerical office operations (classification 8810) sit near the bottom of the rate table. Roofing operations (classifications 5552 and 5553) sit near the top, with approved advisory pure premium rates reaching $21.22 per $100 of payroll for lower-wage workers and $13.60 for higher-wage workers as of September 2025.³ A roofing company with $300,000 in annual payroll is looking at a pure premium base above $40,000 before any insurer markups. An office operation at the same payroll might owe a few hundred dollars.

Getting the classification right matters, and it is checked. The California Department of Insurance lets employers compare manual base rates across carriers using their four-digit classification code.⁴ If workers are misclassified during the policy year, the mistake surfaces at audit and generates back-charges.

The Experience Modification Factor

The experience modification factor, commonly called the Ex-Mod, personalizes the base rate using your own claims history. A factor of 1.00 means your losses match the industry average for your classification. Below 1.00 you get a discount; above 1.00 you pay a surcharge. A business sitting at 0.80 pays 20% less than average. One at 1.50 pays 50% more.

The Workers’ Compensation Insurance Rating Bureau calculates the factor from a defined experience period that begins four years and nine months before your rating effective date and ends one year and nine months before that date.⁵ That window captures roughly three years of claim data, with a gap before the current policy year so older claims have time to develop to their full cost.

This is where the real money moves for most employers. One severe claim can push an Ex-Mod above 1.00 for years, compounding the premium hit across every renewal. Businesses with persistently high modifiers sometimes find that standard carriers will not write the policy at all, which pushes them to the State Compensation Insurance Fund, California’s insurer of last resort and its largest workers’ compensation carrier.⁶

What Gets Added to the Pure Premium Rate

The pure premium rate covers only expected claims costs and the expense of adjusting those losses. Your final policy price has more in it than that.

Every insurer adds a loss cost multiplier that covers administrative overhead, agent commissions, taxes, and profit margin. California Insurance Code § 11732 requires rates to be adequate to cover an insurer’s losses and expenses, while also preventing any single carrier other than State Fund from building a monopoly market share.⁷ Multiple carriers compete for the same risk, and quotes for the same classification and Ex-Mod can vary meaningfully.

Every policy also carries a mandatory Workers’ Compensation Industry Assessment. For 2026, the surcharge is 5.191% of premium. It funds fraud investigations, state oversight, and the administrative machinery of the system. It appears as a separate line item and is an employer-side cost; it never comes out of an injured worker’s benefits.

Between the insurer’s expense loading and the state assessment, your final premium runs well above the pure premium rate on its own. Insurers must file their rating plans with the Insurance Commissioner, and those filings are open to public inspection.⁸

Where Rates Are Heading in 2026

The current statewide average advisory pure premium rate of $1.52 per $100 of payroll took effect September 1, 2025, an 8.7% increase over the prior year.¹ The WCIRB has since proposed advisory pure premium rates effective September 1, 2026 that average 10.4% higher than the current approved rates.⁹ If the Insurance Commissioner approves the proposal at that level, the statewide average would climb to roughly $1.68 per $100 of payroll. The Commissioner can approve, modify, or reject the filing.

The WCIRB operates as the designated rating organization under California Insurance Code § 11750.3, pooling statewide claims and payroll data to produce the advisory rates for each classification.¹⁰

Ways to Lower What You Pay

Your classification code is largely fixed by what you do. The other inputs are more within your control.

Drive down your Ex-Mod. Every claim you prevent keeps your modifier from climbing. A written injury and illness prevention program is the foundation, and return-to-work programs that bring injured employees back in modified roles cut the total cost of each claim, which flows into a lower modifier over time.
Manage open claims actively. Review your loss runs. Insurers sometimes carry inflated reserves on open claims, and those reserves feed into the Ex-Mod calculation. Requesting reserve reviews and getting stale claims closed when appropriate prevents your modifier from drifting upward on paper losses.
Ask about scheduled credits. Many carriers offer scheduled credits or debits of up to 25%, and sometimes more, based on factors like safety programs, management cooperation, and the physical premises. These sit on top of your Ex-Mod and are negotiable at renewal.
Compare carriers. California’s open-rating system means two insurers can quote substantially different prices for the same risk. Brokers who specialize in workers’ compensation can access multiple markets and negotiate.
Consider pay-as-you-go billing. Many insurers tie premium payments to each payroll cycle instead of a large upfront deposit. The total cost does not change, but cash flow improves and audit adjustments at year-end shrink because premium tracks actual payroll in near real time.

Owner Exemptions

Not every person connected to a business has to be covered. Sole proprietors and partners are not considered employees of their own company and are typically exempt. Corporate officers and directors in closely held corporations can opt out, and so can managing members of an LLC. The exemption covers only the owners or principals. If the business has even one other employee, coverage for that employee is still required.¹¹

Licensed contractors file exemption certificates through the Contractors State License Board’s online portal. Certain high-risk license classifications cannot file an exemption at all: C-8 (Concrete), C-20 (HVAC), C-22 (Asbestos Abatement), C-39 (Roofing), and C-61/D-49 (Tree Service).¹² Only an owner, partner, officer, director, or manager of the business can sign the form.

Opting out saves the premium on your own payroll, but it also leaves you without workers’ compensation coverage if you are injured on the job. For owners who work with their hands in hazardous trades, that is a real tradeoff.

The Audit That Decides Your Final Price

The number on your policy at inception is an estimate based on projected payroll. After the policy period ends, the insurer audits your actual payroll records and trues the premium up or down. Hire more people than expected, or pay overtime that pushed payroll above projection, and you owe more. Come in lower, and you get a credit.

The WCIRB also has authority to run test audits of insured employers’ payrolls within one year after a policy expires, checking both the employer’s records and the insurer’s audit.¹⁰ Classifications are verified worker by worker. An employee coded as clerical who actually spent time on job sites will be reclassified to the higher-rated code, and the premium difference is billed retroactively.

Keep detailed payroll records, time cards, job descriptions, and certificates of insurance for every subcontractor you used. Without a subcontractor’s certificate, the auditor adds the payments you made to that sub into your own payroll and charges premium on them as if those workers were your employees. That one gap drives more surprise audit bills than almost anything else.

The audit is also where misclassified independent contractors surface. Under California’s ABC test, every worker is presumed to be an employee unless the hiring business can prove the worker is free from its control, performs work outside its usual business, and operates an independently established trade.¹³ If any prong fails, the worker’s pay gets folded into your classification code and your premium goes up, often with back premium owed.

What It Costs to Go Without Coverage

California treats failure to carry workers’ compensation insurance as a criminal offense. Labor Code § 3700 requires every employer except the state itself to secure coverage, either through an authorized insurer or by obtaining a certificate of consent to self-insure from the Director of Industrial Relations.¹¹

An employer who knowingly operates without coverage commits a misdemeanor under Labor Code § 3700.5. A first conviction carries up to one year in county jail, a fine of at least $10,000 or double the premium that should have been paid (whichever is greater), or both. A second conviction raises the minimum fine to $50,000 or triple the owed premium.¹⁴

The criminal exposure is only one piece. The Division of Labor Standards Enforcement can issue a stop order that prohibits the business from using any employee labor until coverage is secured. Violating a stop order is itself a misdemeanor, carrying up to 60 days in jail or a fine of up to $10,000. Civil penalty assessments can reach $10,000 per employee on the payroll at the time of a compensable injury, capped at $100,000.¹⁵

The quietest consequence may be the worst. When you carry coverage, injured workers are limited to workers’ compensation benefits and cannot sue you in civil court. An uninsured employer loses that exclusive remedy protection. The injured worker can file a workers’ compensation claim and a separate civil lawsuit, with damages that can far exceed what the workers’ compensation system would have paid.¹⁵ Measured against that exposure, even a high premium is the cheaper number.

1
WCIRB California. Insurance Commissioner Issues September 1, 2025 Pure Premium Rate Filing Decision
2
WCIRB California. Standard Classification System
3
WCIRB California. WCIRB Classification and Rating Committee Presentation
4
California Department of Insurance. Workers’ Compensation Rate Comparison
5
WCIRB California. Experience Period
6
State of California. State Compensation Insurance Fund
7
California Legislative Information. California Code Insurance Code 11732
8
California Legislative Information. California Code Insurance Code 11735
9
WCIRB California. WCIRB Bulletins
10
California Legislative Information. California Code Insurance Code 11750.3
11
California Legislative Information. California Labor Code 3700
12
CSLB. Workers Compensation Exemption
13
Franchise Tax Board. Worker Classification and AB 5 FAQs
14
California Legislative Information. California Labor Code 3700.5
15
California Department of Industrial Relations. DWC FAQs for Employers