Workers comp has a peculiarity most other insurance doesn’t: you don’t know the real price until the year is over. The premium you pay upfront is an estimate, and the audit is where the estimate meets reality.
Why the audit exists
Workers comp premium is calculated from payroll, by classification. So much per $100 of payroll for office staff, a different (usually higher) rate for field crews, and so on. Nobody knows a year’s payroll in advance, so the policy starts on projections. After it ends, the carrier audits: actual payroll, by class, with records to back it up. Pay came in higher than projected, you owe more. Lower, you get money back.
For small businesses this is often a mail or online audit, a form plus payroll reports. Larger or higher-risk operations may get a phone or field audit. None of it is an accusation; it’s how the product works.
Where the surprise bills come from
Three patterns account for most audit pain.
Underestimated payroll. The business grew, hires happened mid-year, overtime piled up, and the estimate stayed put. The audit catches the difference all at once, as a bill. The fix is unglamorous: when payroll changes meaningfully mid-year, tell your broker and adjust the policy then, spreading the cost instead of banking it.
Misclassification. Class codes carry very different rates, and the line between “office” and “shop” payroll matters. Sloppy classification in either direction causes trouble: too aggressive and the audit corrects it expensively; too conservative and you overpaid all year. Records that clearly separate duties make this clean.
Uninsured subcontractors. The big one in the trades. Pay a sub who has no workers comp of their own, and the auditor can treat what you paid them as your payroll. A $40,000 sub bill at a field-work rate produces a memorable audit. The defense is simple and absolute: collect a certificate of insurance from every sub before they start, and keep them on file for the auditor.
Making audits boring
The whole game is played before the audit arrives. Estimate payroll honestly at the start of the term. Keep payroll records organized by employee and duty. Separate overtime in your records, since the premium portion of overtime is often excludable. Hold certificates for every subcontractor. Respond to the audit promptly, because noncompliance charges are brutal and entirely avoidable.
We set up workers comp policies with the audit in mind from day one, and we check in before renewal rather than after the audit lands. If your last audit produced a bill you didn’t understand, send it over and we’ll walk through what happened and how to prevent the rerun.