What Is a Workers' Comp Premium Audit?

Every workers' comp policy is sold on an estimate. When you bind coverage, your carrier prices the policy using your projected annual payroll by job classification — a number nobody can know for certain in advance. The premium audit is how the carrier reconciles that estimate against what actually happened over the policy period. It is not optional, it is not a penalty, and it happens on nearly every policy, every year.

Why the audit exists

Premium is calculated as payroll (per $100) multiplied by a class-code rate, multiplied by your experience modification factor, summed across every class code on your policy. At the start of the term, the carrier uses estimated payroll. At the end of the term — or shortly after — the audit substitutes actual payroll and actual class-code assignments for those estimates. If your business grew faster than expected, or your workforce shifted into higher-rated work, you owe an additional premium. If it shrank or shifted into cheaper work, you get a credit. The audit is also the point where your class codes themselves get re-examined, which is where most disputes originate.

Physical audits vs. desk audits

Carriers use two main formats. A physical audit sends a representative (often a contracted third-party auditor, not a carrier employee) to your place of business to review your books directly — payroll ledgers, tax filings, subcontractor invoices — and to ask questions about what each employee actually does day to day. A desk audit (sometimes called a mail or voluntary audit) instead sends you a form to complete and return, occasionally followed by a phone call to clarify entries. Which one you get typically depends on your premium size and industry: smaller, lower-risk accounts are more likely to get a desk audit; larger accounts and higher-hazard trades are more likely to get a physical visit. Either way, the underlying question is the same — does your payroll match your class codes?

The typical timeline

Most audits are triggered by your policy period ending, so the process usually kicks off in the weeks around your renewal date rather than at a random point in the year. A desk audit will state a deadline for returning the completed form — miss it, and some carriers will estimate your payroll on your behalf, which almost never works in your favor. A physical audit is generally scheduled by phone or email in advance, with some flexibility on timing if you need it for a slow season or to have your bookkeeper present. After the auditor finishes their review, expect a written audit summary or worksheet, followed some weeks later by the actual billing adjustment — either an additional premium invoice or a refund. Exact timing varies by carrier, and if you haven't heard back within what feels like a reasonable window, it's worth calling your agent rather than assuming the audit is still pending.

What auditors typically ask for

Whichever format you get, have these ready. Missing documentation doesn't make a charge go away — it usually just means the auditor assumes the least favorable answer for you.

• Payroll records broken out by employee, with enough detail to assign each person (or each person's time) to a class code — not just a single company-wide total.
• Quarterly tax filings (941s or state equivalents) to reconcile total payroll.
• A general ledger or check register showing subcontractor and casual labor payments.
• Certificates of insurance for every subcontractor paid during the period. This is one of the most consequential documents in the whole audit — see our guide on certificates of insurance and subcontractors for why.
• Overtime records that separate straight-time pay from the overtime premium — the extra half in time-and-a-half pay is treated differently in the payroll basis.
• Job descriptions or a short explanation of what each role actually does, especially for any employee coded to a cheaper code like clerical (code 8810) or outside sales.
• The prior policy declarations page, showing what codes and payroll were assumed at binding.
• If you're splitting anyone's payroll across more than one class code, records showing hours or wages by class — without them, an auditor is entitled to put all of that person's payroll in the single highest-rated code that applies.

How the numbers turn into your bill

Once actual payroll is established, the auditor assigns it across your class codes. Most businesses have one governing classification— the code carrying the most payroll — plus any separately ratable operations or standard exceptions (clerical, outside sales, drivers) that qualify for their own, usually cheaper, code. The audit produces a revised premium for the just-completed term; if it's higher than what you paid on estimate, you get an additional premium bill. If your policy renewed before the audit finished, the same corrected payroll and class codes typically carry forward into the new term's estimate too, so an error at audit doesn't just cost you once.

Where mistakes creep in

Two patterns account for most of the disputable dollars we see. First, auditors under time pressure sometimes default everyone to the governing classification instead of checking each person against the standard exceptions — an office employee gets coded at a contractor's trade rate, or an owner who does no hands-on work gets left in a trade code instead of the much cheaper executive-supervisor code (code 5606). Second, documentation gaps get resolved against you by default — no subcontractor COI means that sub's labor gets charged as if they were your employee, and no time-tracking means no payroll split, even where the actual work would have qualified for one. Our article on the seven most expensive class code mistakes walks through these in more detail, and code pages like clerical (8810) and roofing (5551) show just how wide the rate gap can be between a correct and incorrect assignment.

Before the auditor shows up

A few hours of preparation before a physical audit or before you fill out a desk-audit form can materially change the outcome:

• Pull certificates of insurance for every subcontractor you paid this term. If any are missing or expired, try to get a current one before the audit closes.
• Write a one-line job description for every employee, especially anyone coded clerical, outside sales, or executive/supervisory.
• If any employee splits time between two kinds of work, pull whatever time records you have — even partial records are better than none.
• Have your prior year's audit worksheet on hand so you can compare code-by-code.
• If your business grew, shrank, or changed what it does during the year, be ready to explain that in plain terms — auditors work faster, and more accurately, when they understand the story behind the numbers rather than just the numbers themselves.

During the audit itself

If a physical auditor proposes a classification you disagree with on the spot, you're not obligated to accept it in the room. It's reasonable to say you'd like to review the worksheet before signing anything, and to follow up in writing once you've had a chance to compare it against your own records. Auditors are generally working through a lot of accounts and doing their best with the information in front of them — a respectful, specific, written follow-up citing your own documentation is usually far more effective than an on-the-spot argument.

If the bill looks wrong

You're not stuck with whatever the auditor decided. Carriers have a formal dispute process, and classification errors are commonly recoverable retroactively for a period typically cited around three years — though the exact window depends on your carrier and state. Our step-by-step guide on how to dispute a workers' comp audit covers the evidence to gather and who to contact first.