Workers' Compensation Insurance Cost: What Drives the Rate

The basic formula

Workers' comp premium = (class code rate per $100 of payroll) × (payroll in $100s) × (experience modification factor). That's the entire base equation. From there, carriers add or subtract schedule credits, expense constants, and state-specific surcharges, but the formula above explains ~85% of the price.

Class codes drive the rate

Class codes are the single biggest lever. Office staff might be coded at $0.20 per $100 of payroll. Roofers can be $25+ per $100 of payroll. The difference between a correct and incorrect class code can be a 10–80x change in price.

We routinely re-class clients into the correct code at renewal and recover material premium for operations that were over-coded by a prior agent — especially in mixed-trade contractor accounts.

The experience mod

After about three years in business, your operation gets an experience modification factor (e-mod) that rewards or penalizes you based on actual loss history vs. the class average. A 0.85 mod means you pay 15% less than the class average. A 1.100+ mod means you pay 25% more.

The mod is calculated by NCCI or a state rating bureau — not by the carrier. We can audit your mod calculation, dispute open reserves, and help close out stale claims that are pushing your mod higher than it should be.

Audit time

Workers' comp premium is estimated at bind and audited at the end of the policy. If actual payroll is higher than estimated, you owe more. If it's lower, you get refunded. The two biggest audit traps: (1) including 1099 subs without certificates as payroll, and (2) failing to break out payroll between class codes.