Premium Basis, Experience Modification, and Classification

Premium Is Built on Payroll

Workers comp premium is not a flat charge. The fundamental formula is:

Premium = (Payroll / 100) x Rate

The rate is stated per $100 of payroll and varies by classification code (the type of work). Clerical office workers carry a low rate; roofers carry a high rate, because their injury frequency and severity differ enormously. NCCI publishes the classification codes and manual rates.

Because payroll is the basis, the premium charged at policy inception is an estimate using projected payroll. At expiration the insurer conducts a payroll audit; if actual payroll exceeded the estimate, the insured owes additional premium; if it was lower, the insured receives a return premium.

Classification: Governing Class vs. Standard Exceptions

Each business is assigned a governing classification reflecting its principal operation, plus separately rated classes for distinct exposures. Certain job titles are standard exception classes rated on their own everywhere — most importantly clerical office (8810), outside salespersons (8742), and drivers. These are split out because their low risk should not be blended into a high-risk governing class.

Misclassification is a common exam trap: putting a roofing crew in the clerical class to lower premium is rate evasion, not a legitimate split.

The Experience Modification Factor (Mod)

Larger employers are individually rated through the experience modification factor (Mod or EMR), which compares the employer's actual losses to the expected losses for its class.

• Mod = 1.00 -> the employer is average for its class.
• Mod below 1.00 (e.g., 0.85) -> better than average; premium is reduced (a credit).
• Mod above 1.00 (e.g., 1.20) -> worse than average; premium is surcharged.

The Mod multiplies the manual premium:

Modified Premium = Manual Premium x Mod

The experience-rating plan also weights frequency more heavily than severity — many small claims hurt the Mod more than one large claim — because frequent losses better predict future losses. This is why claims frequency matters so much to an employer's cost.

Worked Numeric: From Payroll to Final Premium

A contractor has $600,000 of governing-class payroll at a manual rate of $8.00 per $100, plus $200,000 of clerical (8810) payroll at $0.40 per $100. Its experience Mod is 0.90 and it qualifies for a 5% schedule credit.

1. Governing manual premium = ($600,000 / 100) x $8.00 = $48,000.
2. Clerical manual premium = ($200,000 / 100) x $0.40 = $800.
3. Total manual premium = $48,000 + $800 = $48,800.
4. Apply Mod: $48,800 x 0.90 = $43,920.
5. Apply 5% schedule credit: $43,920 x 0.95 = $41,724 estimated annual premium.

Note the order: manual -> experience mod -> scheduled/other rating modifications. If year-end audited payroll differs, the whole calculation is re-run on actual figures.

Dividend Plans, Retro, and Loss Control

Employers can further shape cost through optional plans:

• Dividend plans (participating): if the group's or the insured's loss experience is good, the carrier returns a dividend after the policy year. Dividends are never guaranteed in advance (state law forbids guaranteeing them).
• Retrospective rating (retro): final premium is adjusted after the period based on the insured's actual losses, between a stated minimum and maximum premium. Rewards good loss control but exposes the insured to higher cost in a bad year.
• Loss-control / safety programs: reduce claim frequency, which directly improves the Mod over time.

Tie it together: payroll sets the base, classification sets the rate, the Mod rewards or penalizes actual experience, and dividend/retro plans share risk further.

Premium Audit Mechanics

Because payroll is the exposure base, the audit is central to workers comp. At policy inception the insurer charges a deposit (estimated) premium based on projected payroll. After expiration it conducts a final audit — physical, voluntary (mail/phone), or self-reported — to capture actual remuneration, then issues an additional or return premium.

Auditable payroll includes wages, salaries, commissions, bonuses, holiday and vacation pay, and the value of certain in-kind compensation. It generally excludes items like tips, group-insurance premiums paid by the employer, and severance. Overtime is included at straight-time wages only — the premium portion (the extra half-time) is excluded. Misreporting payroll or refusing an audit lets the insurer estimate payroll and bill accordingly, and is a frequent source of premium disputes.

How Experience Rating Builds the Mod

The experience mod is calculated by NCCI (or the state bureau) from the employer's actual losses and payroll over a three-year window, excluding the most recent policy year. The plan compares actual primary and excess losses to expected losses for the class. A crucial feature: each individual loss is split into a primary portion (the first slice, fully counted) and an excess portion (heavily discounted). This is why frequency — many small claims, each contributing a full primary value — drives the mod up faster than a single catastrophic claim whose excess portion is largely discounted.

Only employers whose premium exceeds an eligibility threshold are experience rated; smaller employers pay manual rates. The practical lesson for risk management is direct: preventing small, frequent claims through safety programs, return-to-work plans, and prompt claim handling lowers the mod and compounds savings year after year, because each improved year eventually rolls into the rating window.