13.3 Premium Basis, Experience Modification, and Classification

How WC Premium Is Built

Workers compensation premium is payroll-driven. The premium basis is remuneration (payroll), expressed per $100 of payroll. NCCI (or an independent state rating bureau) assigns each type of work a classification code and publishes a manual rate per $100 of payroll for that class.

Base (manual) premium formula:

Manual Premium = (Payroll / 100) x Manual Rate

Because the policy is written on an estimated payroll at inception, WC is an auditable policy: a payroll audit at the end of the term reconciles actual payroll to estimated payroll, producing an additional premium or a return premium.

Classification Rules

• The governing classification describes the employer's overall business; most payroll is assigned to it.
• Standard exceptions (clerical office, outside salespersons, drivers) are split out into their own lower-rated codes regardless of the business.
• Payroll used for rating is generally capped for certain executive officers and may exclude overtime premium pay (only the straight-time portion of overtime counts in most states).

Misclassifying a high-hazard payroll into a low-rated clerical code is both a rating error and, if intentional, premium fraud. The audit exists to catch this.

Worked Example: Manual Premium

A carpentry contractor has estimated annual payroll of $600,000 in a class with a manual rate of $8.50 per $100 of payroll, plus a clerical office payroll of $80,000 rated at $0.40 per $100.

Carpentry: ($600,000 / 100) x $8.50 = $51,000. Clerical: ($80,000 / 100) x $0.40 = $320. The split lowers cost - lumping the clerical payroll into carpentry would have cost ($80,000/100) x $8.50 = $6,800 instead of $320.

Experience Modification (Mod / EMR)

Larger employers are experience rated. The experience modification factor (the mod or EMR) compares the employer's actual losses to the losses expected for a business of its size and class:

Modified Premium = Manual Premium x Experience Mod

• A mod of 1.00 is average (expected losses).
• A mod below 1.00 (e.g., 0.85) means better-than-expected loss experience -> a credit (lower premium).
• A mod above 1.00 (e.g., 1.20) means worse-than-expected experience -> a debit (higher premium).

The mod rewards safety and is a powerful incentive. Frequency of claims affects the mod more than a single large severe claim because rating plans discount large losses.

Worked Example: Applying the Mod and Plans

Using the $51,320 manual premium above, assume an experience mod of 0.85 and then a 15% schedule credit for documented safety controls.

1. Apply the mod: $51,320 x 0.85 = $43,622 modified premium.
2. Apply schedule credit: $43,622 x (1 - 0.15) = $37,078.70.

Order matters on the exam: experience mod is applied to manual premium first, then premium discount / schedule rating / expense constant adjustments. A premium discount (volume discount on large premiums) and a retrospective rating plan (premium adjusted after the term based on actual losses subject to a min/max) are common large-account options.

Premium Audit, the Mod Below 1.0, and Retrospective Rating

WC premium starts as an estimate (estimated payroll × rate per $100 ÷ 100, by classification) and is trued up by a premium audit at the end of the term, so the final premium reflects actual payroll — a frequent exam point when payroll grows mid-term. The experience modification factor (EMR) compares the employer's actual losses to expected losses for its class: a mod below 1.0 is a credit (better-than-average safety) and above 1.0 is a debit. The mod multiplies the manual premium, so a $51,320 manual premium at a 0.85 mod yields about $43,622 before other adjustments.

Larger employers may use retrospective rating, where the final premium is calculated after the period based on actual losses, subject to a minimum and maximum premium — rewarding loss control directly. Schedule rating and premium discounts for size further adjust the figure. Officers and partners may elect in or out of coverage, changing the payroll base, a detail that affects both premium and benefits eligibility.

Audit, Minimum Premium, and the Mod Direction Recap

WC premium is an estimate trued up by audit, so the final bill reflects actual payroll across each governing classification rather than the estimated figure — a point tested when a business adds employees mid-term. A minimum premium applies even to tiny payrolls to cover the insurer's fixed costs. The experience modification factor is the key lever: a mod above 1.0 is a debit (worse-than-expected losses raise premium), a mod below 1.0 is a credit (strong safety lowers it), and a mod of exactly 1.0 is average.

Multiply the manual premium by the mod, then apply schedule credits/debits and premium discounts. Retrospective rating ties the final premium directly to the period's actual losses between a stated minimum and maximum, giving large employers the strongest financial incentive to control claims.

Rating Plans and Officer Election Recap

Beyond the manual-rate-times-mod calculation, the exam expects familiarity with the rating plans that adjust final premium: premium discount (a credit recognizing that larger premiums carry proportionally lower expense loadings), schedule rating (debits or credits for risk-specific factors such as safety programs or hazardous machinery), and retrospective rating (final premium set after the term from actual losses, bounded by a minimum and maximum).

A frequently tested administrative point: executive officers, sole proprietors, and partners may elect to be included in or excluded from coverage, which changes both the payroll used in the premium base and their own eligibility for benefits — so excluding officers lowers premium but leaves them without WC protection.