How workers' comp audit premium is calculated
A workers' compensation policy is priced at the start of the term on payroll that hasn't happened yet. The business supplies an estimate by class code, and premium is billed on it across the year. The audit replaces every estimate with the payroll actually paid, and recalculates.
The carrier's arithmetic runs per class code: payroll divided by 100, times the rate for that code (rates are quoted per $100 of payroll), times the experience modifier, summed across every code, then compared to what was already billed. The result is either additional premium owed or return premium coming back.
The estimator above deliberately does something simpler. It takes the premium you were charged per dollar of estimated payroll and applies that same rate of premium to the payroll you actually paid. The class code rates and the modifier are already inside the premium charged, so there is nothing to look up and nothing to split by class. Three numbers, one answer, and a clear sense of which direction the audit is heading.
That simplicity is the point. The audit is the carrier's job, performed from your actual records. This is the number to have in mind before the invoice arrives, not a substitute for it.
Why the carrier's number will differ from this estimate
The estimator models the core calculation only. A carrier's final audited premium includes adjustments that depend on your policy, your state, and decisions the auditor makes from your records. Any of these can move the figure:
- Uneven growth across class codes. The estimate assumes payroll moved evenly. If a high-rated trade grew while clerical stayed flat, the real change is larger; the reverse is smaller.
- Minimum premium and expense constant. A policy has a floor. If recalculated premium falls below it, the minimum applies.
- Schedule credits, debits, and premium discount. Underwriting adjustments applied as percentages on top of manual premium.
- State assessments and surcharges. Added by statute and varying by state.
- Officer and owner payroll limits. Included officers are rated between a state minimum and maximum rather than at actual pay.
- The overtime premium exclusion. Applied only if payroll records separate overtime from regular wages.
- Uninsured subcontractor payments. Added to payroll where no certificate of insurance covers the work dates. Often the largest single adjustment.
- Classification changes. The auditor assigns class codes from actual duties, and may move payroll between codes with different rates.
None of these is unusual. They are the reason the audit is performed by the carrier rather than calculated by the insured. The estimate is for preparing, so that the invoice, when it arrives, is not a surprise in direction or rough size.
Additional premium versus return premium
| Audited payroll came in | Result | Typical cause |
|---|---|---|
| Higher than estimated | Additional premium owed | Growth, new hires, subcontractors without certificates |
| Lower than estimated | Return premium or credit | Slower hiring, a bid that never became a job, a dropped service line |
| About the same | Small adjustment either way | Class code corrections, exclusions applied |
If the audit invoice looks wrong
Compare it line by line against your own payroll by class code. Check that the overtime exclusion was applied if your records supported it, that officer caps were used, and that every subcontractor charge corresponds to a genuinely missing certificate. Then raise the specific discrepancy with the carrier's audit department in writing, with documents attached. Disputes that name a line item and supply the record behind it get resolved; general objections do not.
Frequently asked questions
How is workers' comp audit premium calculated?
The carrier takes audited payroll for each class code, divides by 100, multiplies by that code's rate and by the experience modifier, and compares the total to the premium already billed. This estimator uses a simpler proportional version: the premium you were charged per dollar of estimated payroll, applied to the payroll you actually paid. Rates and the modifier are already inside the premium charged, so you don't have to look them up.
Why will my actual audit bill differ from this estimate?
Because the estimate assumes payroll grew or shrank evenly across your class codes, and because the carrier applies adjustments it cannot see: class code changes from actual duties, uninsured subcontractor payments added as payroll, the overtime premium exclusion, officer payroll minimums and maximums, minimum premium and expense constant, schedule credits, and state assessments. The estimate gives direction and rough size, not the final number.
Will I get money back if my actual payroll was lower than estimated?
Usually, yes. If audited payroll comes in below the estimate the policy was written on, the recalculated premium is lower and the difference is returned or credited. Minimum premium rules can limit how far it drops, and any prior balance on the account is applied first.
What is the difference between estimated payroll and actual payroll?
Estimated payroll is the figure the policy was priced on at the start of the term, projected before the year happened. Actual payroll is what the business paid during the policy period, verified at audit against payroll reports and quarterly 941 filings. The audit exists to replace the first with the second.
What should I do if the audit invoice looks wrong?
Compare it line by line to your own payroll records by class code, check whether the overtime exclusion and officer caps were applied, and confirm every subcontractor charge is backed by a missing certificate. Then raise the specific discrepancy with the carrier's audit department in writing, with the supporting documents attached.
Preparing for the audit itself? The audit checklist generator lists every document you'll be asked for, and the subcontractor exposure calculator puts a figure on the most common adjustment.