13.3 Premium Basis, Experience Modification, and Classification

Premium Is Built From Payroll and Classification

Workers' compensation premium is not a flat charge. It is computed from the employer's payroll (the premium basis) multiplied by a rate per $100 of payroll assigned to each job classification code. Most states rely on the National Council on Compensation Insurance (NCCI) for classifications, rates/loss costs, and the experience-rating plan; a few states (e.g., California with the WCIRB) use independent bureaus.

The core manual-premium formula is:

Manual premium = (Payroll / 100) x Rate per $100

Payroll for premium purposes is estimated at inception and adjusted at a final premium audit after the policy period ends.

Classification Codes

Each employee's payroll is assigned to a four-digit class code describing the work's hazard (e.g., clerical office staff carry a low rate; roofers carry a very high rate). Rules of thumb tested on exams:

• An employer is generally assigned to the governing classification that best describes the overall business, with separately rated standard exception classes (clerical, drivers, outside sales) split out.
• Higher-hazard codes carry higher rates per $100 of payroll.
• Misclassification — coding a roofer as clerical — is a serious audit and fraud issue and inflates or understates premium.

Worked Manual-Premium Example

Assume a small contractor:

Clerical: ($200,000 / 100) x $0.30 = $600. Carpentry: ($500,000 / 100) x $8.00 = $40,000. The combined manual premium is $40,600 before any experience modification, schedule credits, or premium discounts.

The Experience Modification Factor (Mod)

Larger employers are experience rated. The experience modification factor (EMR or "mod") compares an employer's actual losses to the expected losses for businesses of its size and class, then adjusts premium up or down.

• Mod = 1.00 -> average loss experience; no change.
• Mod < 1.00 (e.g., 0.85) -> credit mod; better-than-average safety; premium reduced.
• Mod > 1.00 (e.g., 1.20) -> debit mod; worse-than-average losses; premium increased.

A defining feature: experience-rating plans weight frequency over severity. Many small claims hurt the mod more than one large claim of the same total dollars, because frequent losses are treated as more predictable and controllable.

Applying the Mod and a Final-Premium Worked Example

The standard order: manual premium x experience mod, then schedule/experience credits and premium discount, plus an expense constant.

Worked numeric: Using the $40,600 manual premium above with a debit mod of 1.20:

Modified premium = $40,600 x 1.20 = $48,720

If instead the contractor earned a credit mod of 0.85:

Modified premium = $40,600 x 0.85 = $34,510

The difference between the debit and credit outcomes ($48,720 vs $34,510) is $14,210 on the same payroll — a powerful incentive for loss control. Final premium is settled at audit, where the insurer reconciles estimated payroll against actual payroll and bills or refunds the difference.

Premium Built From Payroll, Class Code, and Rate

WC premium is computed per $100 of payroll by job classification code (NCCI or state). Each class carries a manual rate reflecting that occupation's hazard — a clerical class (low rate) versus a roofing class (high rate). The base (manual) premium is:

Manual Premium = (Payroll ÷ 100) × Manual Rate, summed across all classifications.

Employees are assigned to the class that describes the business operation, with separately rated standard exceptions (clerical, drivers, outside sales) split out.

Worked Manual-Premium Example

A contractor has $600,000 carpentry payroll at a manual rate of $8.00 and $200,000 clerical payroll at $0.30.

• Carpentry: (600,000 ÷ 100) × 8.00 = 6,000 × 8 = $48,000.
• Clerical: (200,000 ÷ 100) × 0.30 = 2,000 × 0.30 = $600.
• Manual premium = $48,600 before the experience modifier.

The Experience Modification Factor

The experience mod (X-mod) compares an employer's actual losses to expected losses for its class size over a three-year window:

• Mod = 1.00 — average; no change.
• Mod < 1.00 (credit) — better-than-average loss experience reduces premium.
• Mod > 1.00 (debit) — worse-than-average increases premium.

The mod rewards safety and is why WC insureds invest in loss control.

Applying the Mod and Final Premium

Continue the example with a mod of 0.85 (a 15% credit) and a schedule/premium discount ignored for simplicity:

Modified premium = $48,600 × 0.85 = $41,310.

A mod of 1.20 instead would raise it to $58,320. The exam expects you to multiply manual premium by the mod, recognizing that a sub-1.0 mod is a credit and a >1.0 mod is a debit. Final premium is then adjusted by premium discount (volume) and any schedule rating, and reconciled at audit when actual payroll is verified — WC is an auditable, estimated-then-adjusted premium line.

Premium Audit and the Estimated-Then-Adjusted Cycle

Workers comp premium is auditable: the policy begins on an estimated annual payroll, and at expiration the insurer conducts a premium audit of actual payroll records to compute the earned premium, billing additional premium or refunding overpayment. Employers who refuse audit access may be charged an estimated (default) premium. The exam tests this estimate-now, true-up-later cycle as a defining feature of WC (and of general-liability payroll/sales-based rating).

Schedule Rating, Premium Discount, and Deposit

Beyond the experience mod, final WC premium reflects schedule rating (debits/credits for specific risk characteristics like safety programs or housekeeping), a premium discount that lowers the rate per dollar as premium size grows (recognizing fixed expenses spread over a larger base), and an expense constant plus minimum premium. A deposit premium is collected at inception. The ordering on the exam is: manual premium → experience mod → schedule rating → premium discount, with audit reconciling the estimate to actual payroll.

A stem listing several adjustment factors tests whether you apply the mod before discount and recognize audit as the final reconciliation.