13.3 Premium Basis, Experience Modification, and Classification

How Workers Comp Premium Is Built

Workers comp premium is payroll-based. The premium for each job classification equals the rate per $100 of payroll multiplied by the payroll for that class:

Premium = (Payroll / 100) x Rate

Classifications are governed by the NCCI (National Council on Compensation Insurance) class code system (independent bureaus apply in monopolistic and some independent states). Each occupation receives a four-digit class code and a manual rate reflecting its hazard. Clerical work carries a low rate; roofing carries a high rate.

Worked Classification Premium

A contractor has two classes of payroll:

Total manual premium = $600 + $40,000 = $40,600. This is the starting point before the experience modification factor and any schedule or expense adjustments are applied.

Experience Modification (the 'Mod')

The experience modification factor (EMR or 'mod') compares an employer's actual loss history to the expected losses for businesses of its size and class. It is then multiplied against manual premium:

Modified premium = Manual premium x Experience mod

• A mod of 1.00 is exactly average.
• A mod below 1.00 (a credit mod) means better-than-average losses and lowers premium.
• A mod above 1.00 (a debit mod) means worse-than-average losses and raises premium.

The mod is a powerful loss-control incentive: improving safety lowers the mod, which lowers premium for years afterward.

Worked Mod Calculation and the Audit

Using the $40,600 manual premium above, apply an experience mod of 0.85 (a credit):

$40,600 x 0.85 = $34,510 modified premium.

Now apply the same manual premium with a debit mod of 1.20:

$40,600 x 1.20 = $48,720 modified premium.

Because premium depends on payroll the employer cannot know exactly in advance, workers comp is an auditable policy. The insurer charges an estimated deposit premium at inception and conducts a premium audit after the policy period to compare actual payroll to the estimate, generating either an additional premium bill or a return premium. Trap: owners and officers may be subject to minimum and maximum payroll caps for rating - not their full salary.

How Workers Compensation Premium Is Built

Workers compensation premium starts from payroll, not from a coverage limit. The insurer assigns each type of work a classification code with a manual rate expressed as dollars per 100 dollars of payroll, reflecting the hazard of that work. The basic premium equals (payroll divided by 100) times the manual rate, summed across all classifications, then adjusted by the experience modification factor and any schedule or premium discounts. Because premium tracks payroll, the policy is auditable: a deposit premium is paid up front and a final audit reconciles actual payroll at the end of the term.

Worked Classification Premium

Suppose a contractor has 600,000 dollars of carpentry payroll at a manual rate of 8.00 per 100 and 200,000 dollars of clerical payroll at 0.30 per 100. The carpentry premium is 600,000 / 100 times 8.00 = 48,000 dollars; the clerical premium is 200,000 / 100 times 0.30 = 600 dollars; the manual premium is 48,600 dollars before the experience modifier. Clerical work carries a far lower rate than carpentry because the hazard is lower, which is why proper classification (and not lumping all payroll into the highest class) matters enormously to the insured.

The Experience Modification Factor

The experience modification (the mod) compares an insured's actual past losses to the expected losses for its classification and size. A mod of 1.00 is average; below 1.00 (a credit mod) means better-than-expected loss experience and lowers premium; above 1.00 (a debit mod) means worse experience and raises premium. The mod rewards loss control and is one of the strongest financial incentives for workplace safety, because a single large claim can raise the mod for several years, compounding the direct cost of the claim with higher future premiums.

Worked Mod Calculation and the Audit

Applying a 1.15 debit mod to the 48,600-dollar manual premium yields 48,600 times 1.15 = 55,890 dollars; a 0.85 credit mod would yield 41,310 dollars, a swing of more than 14,000 dollars driven entirely by loss history. After the policy term, the insurer conducts a premium audit, examining payroll records to determine actual exposure; if payroll exceeded the estimate, the insured owes additional premium, and if it was lower, the insured receives a return. The exam tests the payroll-times-rate calculation, the meaning of credit versus debit mods, and the auditable nature of the premium.

Scheduled and Retrospective Rating Plans

Beyond the experience modifier, larger employers may use schedule rating, which adjusts premium up or down for individual risk characteristics such as management safety programs, equipment condition, and employee training, within filed credit and debit ranges.

Very large employers may use a retrospective rating plan, where the final premium is calculated after the policy period based on the insured's actual losses during the term, subject to a minimum and maximum premium. Retrospective rating gives the insured a direct financial stake in loss control, because good experience lowers the retro premium toward the minimum while poor experience raises it toward the maximum.

Premium Audit and Recordkeeping

Because the deposit premium is only an estimate, accurate payroll records by classification are essential at audit. Misclassified payroll, unrecorded subcontractors, or overtime treated incorrectly can produce large audit adjustments, so the exam expects you to understand that the auditable nature of the policy makes recordkeeping a core compliance duty.