Workers' Comp Premium Audit: What the Auditor Checks and How to Keep the Bill Honest

Nobody likes the premium audit letter. Your policy ended, the carrier wants your payroll records, and a few weeks later a bill shows up for additional premium. Sometimes it's a credit. Either way, most employers treat the number as final and pay it. That is a mistake. The premium audit is one person's review of your records against a long rulebook, and when it goes wrong, it almost never goes wrong in your favor.

Start with what this is and what it isn't. The carrier's premium audit is a payroll exercise. The auditor verifies how much you paid, who did what work, and whether the classification and payroll rules were applied correctly. They do not look at your claims, your loss runs, or your reserves. If your premium is high because of losses, that is a claims problem and a different kind of review. This guide is about the payroll side: the audit, the bill, and how to keep it honest.

What the auditor actually reviews

The auditor rebuilds your premium from your records. Five things get checked:

• Payroll by class code. Every employee's wages land in the classification that matches the work they actually do. When duties have drifted since the policy started, this is where the trouble begins.
• What counts as payroll. Not everything you paid counts. The premium portion of overtime (the extra half in time-and-a-half) is generally excludable. Regular wages, bonuses, and vacation and sick pay generally count. Severance and a few other categories have their own rules, and they vary by state.
• Subcontractors. For every sub you paid, the auditor wants a valid certificate of insurance covering the policy period. No certificate, and the carrier adds what you paid that sub to your own payroll, usually at a high-rated class. This single item produces some of the biggest surprise bills in the business.
• Who counts as an employee. A 1099 does not settle it. The auditor applies employment tests, and workers you treated as contractors can end up on your payroll for premium purposes.
• Which state. If you work in more than one state, payroll has to sit in the right one, under the right state's rules.

The five errors that inflate the bill

The same five errors show up again and again. Every one of them costs the employer, never the carrier.

• Misclassified employees. The office manager coded to a field classification. The delivery driver coded with the warehouse crew. Duties drift over a policy year and nobody updates the codes. This is the most common error and often the most expensive.
• Overtime that was never backed out. The overtime premium is excludable in most states, but only if your payroll records show it separately. One lump "gross wages" number and the auditor includes all of it.
• Missing subcontractor certificates. The sub had insurance, but the certificate never made it into your files, or it expired mid-job and nobody noticed. Without paper, the payroll gets added to yours.
• Pay that shouldn't have counted. Severance, certain statutory payments, and a handful of other categories don't belong in premium payroll, but they land there when nobody flags them.
• Estimated payroll. When records are incomplete or the auditor can't verify a number, they estimate. Estimates are built to protect the carrier, not you. Clean records are the only defense.

How to prepare before the auditor arrives

The audit goes better when you're ready before the letter arrives. None of this is complicated; it's just organization.

• Keep payroll by employee, by pay period, with overtime shown separately. If your payroll system can split straight time from the overtime premium, turn that on now.
• Review class codes against actual job duties once a year. Walk the floor, literally or on paper, and ask what each group of people really does all day.
• Collect subcontractor certificates before work starts and diary the expiration dates. A certificate that lapsed for two months is a two-month gap the auditor will price.
• Learn your state's exclusion rules, or have someone who knows them review your setup. The rules on what's excludable are specific and they change.

How to dispute the findings

The auditor's number is a starting point, not a verdict. If the bill looks wrong, push back, and do it with paper.

• Ask for the workpapers. You're entitled to see how every number was derived: which payroll, which class, which rule. Vague bills get specific fast when you ask for the math.
• Reclassify with evidence. Job descriptions, org charts, and time records beat the auditor's assumptions. If the duties don't match the code, say so and prove it.
• Produce late certificates. A certificate that arrives after the audit can still get subcontractor payroll removed. Don't assume a missed deadline is final.
• Mind the clock. Dispute promptly and in writing. Once you've paid without objection, reopening the audit gets much harder.
• Bring your broker. A good broker has disputed a hundred of these and knows which underwriters will deal. If yours won't help, that's information too.

What a premium audit won't fix

Honest boundaries. The premium audit only prices the payroll you had. It won't lower your experience mod, it won't fix your claims handling, and it won't make your safety program better. If your premium is climbing because of losses rather than payroll errors, you need the claims-side review, not a payroll fight. The two problems feel the same on the invoice and they're solved differently.

Where an independent review fits

There are two moments when a second set of eyes pays for itself. Before the audit: reviewing your classifications, payroll setup, and certificates so the auditor sees clean records and has nothing to estimate. And after the bill: reviewing the auditor's workpapers against your records to find what they got wrong. That review is document work, not opinion. Your payroll records against their math, line by line.

CompShield is a workers' compensation claims-defense and cost-control firm. This guide describes the workers' comp premium audit in general terms and is not legal, insurance, or accounting advice. Payroll, classification, and audit rules vary by state; verify current requirements for your jurisdiction.