An audit for workers compensation is when your insurer reviews exactly how much you paid workers during the policy year after the year has ended. Premiums you paid all year were only estimates so the audit replaces them with a final number and bills you for any difference or refunds money if appropriate. You agreed to that review when you bought the policy, and refusing it costs much more than enduring that review.
An audit is not a sign your insurer suspects you. An audit is simply a normal process of settling all workers comp policies. The money, though, rarely turns on what you claimed as payroll but rather on the people you did not claim as payroll (mostly subcontractors) and what job codes are assigned to each employee by the auditor.
Workers Comp Premium Audit
Premium audits are your insurance company's review of all payroll records at the end of a given policy term. After reviewing those payroll records, an audit determines your final workers compensation premium based on what you actually paid your people and the specific job duties performed by each employee. Your insurance company will bill you for any amount above the estimated premium you paid throughout the year and will refund to you any overpayment made as part of your annual premium.
What is a workers comp audit and why is your premium only an estimate?
A workers comp audit assesses the three factors (exposures) that drive your bill. As such, this assessment will replace the "estimate" that you paid with the final premium those exposures produce. Workers comp rates are based upon each $100 of payroll, so the first page of your workers comp policy (the Information Page), which includes your estimated annual payroll, was only a projection of a payroll period that has never existed. That page is the workers comp version of a declarations page. Payroll also means more than base wages. Your workers comp policy considers all types of remuneration to include base salary, bonus payments, commission payments, vacation pay.
Your Policy states the same thing. Section titled "Premium", numbered "Part Five", will tell you that the amount listed is an estimate, and it will be determined by actual payroll at the end of the term. Also, the insurance company has the right to audit your records for up to three (3) years from the date the policy ended, so a closed policy does not mean completed. Our workers compensation guide walks through Item 4 of that page, the rate and classification table.
What does the auditor examine?
All requests by auditors for records related to Workers Compensation audits will check (1) how much you paid, (2) who performed what work, or (3) if your subcontractors had their own Workers Compensation coverage. It is the second test that relies upon class codes, those number systems that tie work to a particular rate, thus explaining why a roofer pays many times as much per dollar of payroll compared to a bookkeeper. Auditors do not rely on your summaries, but rather use source documents and cross reference them with each other:
| Records requested | What the auditor is testing |
|---|---|
| Payroll journals, quarterly federal payroll tax returns (the 941s), state unemployment returns | To ensure that the payroll amounts you report match the actual payroll you paid and already submitted to tax authorities |
| Job descriptions, payroll split by employee and duty | To verify that all employees are classified correctly in their respective class codes, and if there is a splitting of an individual's wages into two or more class code categories, that the supporting documentation exists |
| Overtime records | That the extra portion of overtime pay is identified separately, so it can be excluded where your state allows |
| Subcontractor ledger and certificates of insurance | That each subcontractor carried its own Workers Compensation Insurance for the entire duration of time they performed work for you |
| General ledger, cash disbursements | That there is no hidden labor cost off payroll, in casual labor or 1099 payments |
Of these, two tests have monetary value. If an auditor has no record of how a split of a payroll occurred they will place an entire employee into the highest rated classification that applies, and without a certificate of insurance provided by a subcontractor, all of the subcontractor's payroll costs will be assigned to you.
A certificate is one page of evidence from your sub's insurance company, and it counts only if it includes the sub's name and shows coverage active through all the days they were working for you. Have yourself named (as the certificate holder) on that cert so that you receive notice when their policy cancels during your job.
What are the most common audit surprises?
Most of the additional premium comes from these three patterns, and paperwork you can collect months earlier beats all three:
- An uninsured subcontractor becomes your employee: If there is no valid certificate within this file, the sub's payroll will be included with yours on the audit. The auditor will charge you based upon the total contract price if you cannot provide documentation of that payroll. Hire an uninsured subcontractor and state law usually makes you the employer of its injured workers anyway. Thus, you carried the risk of injury for the entire year regardless.
- The clerical code stops applying: Generally, most owners believe that as long as an individual works out of a "desk" at some point during their employment, then they fall under the code for offices (8810). They do not. For example, if you have an employee working out of the office designated by the code 8810 and they are assigned to pull stock or visit other job sites, then that person will be classified under the same code as the majority of your operations, the governing classification, and the auditor only needs to see this once.
- Overtime stays in the number: Most states permit you to exclude the premium part of the overtime, (the amount over straight time), but only if there is a record to show that the overtime is separately calculated. Otherwise, report gross wage in one column and you pay premiums based upon the increased gross wage. Severance is subject to this same trap, as are any officers' salaries above your State's maximum.
What happens if you ignore the audit?
Ignoring the audit turns it from a paperwork issue into a financial one. If you refuse to provide requested documentation, you are breaking your commitment established in Part Five, and most policies have another page attached for this purpose. This document is the Audit Noncompliance Charge Endorsement (form number WC 00 04 24) and if permitted by the State, your carrier may impose a penalty on you based upon your estimated annual premium. In general, the amount imposed is a multiple of your estimated annual premium, commonly up to two times. You should read the actual multiplier off your own copy of the endorsement.
California has written this penalty into statute and it is bigger than the others. Under Insurance Code Section 11760.1, if an employer has refused to allow the insurer access to its records after the insurance company's third request over a period of at least 90 days, then that employer will be liable for three times the carrier's current estimate of the annual premium for the policy.[1] Your carrier can also cancel outright for refusing to cooperate. This termination is carried forward into the marketplace, because when you go to get another carrier, they know why the previous carrier terminated your coverage.
How do you prepare for a workers comp audit and dispute the bill?
Good audits start at the beginning of the policy year, not just weeks before auditors call. Summarize payroll by employee and class code by state and keep overtime on its own line and reconcile that to quarterly 941 filings each quarter rather than waiting until year end. Collect a subcontractor certificate before anyone starts swinging hammers. During the audit hand over exactly what is asked for and nothing more because auditors test whatever comes to them.
To dispute the results of a premium audit, ask the auditor for their worksheets first because all arguments you can make about a summary bill will go nowhere. The worksheets, or work papers, are what detail how employees were placed in codes and who was included as a subcontractor. In writing, identify each disputed item to your carrier's premium audit department with evidence attached, and watch the dispute window, often 60 days. Pay the undisputed portion of the bill while the rest is pending.
A classification that your carrier will not address goes over the carrier. Classification codes are created and enforced by a rating bureau, NCCI in most states and the WCIRB in California. The rating bureau determines if a given code is appropriate for your type of business. If the rating bureau's determination of the appropriateness of the code does not stand the test in California, Insurance Code Section 11737 allows you to appeal to the Insurance Commissioner regarding their determination.[2] Beyond this audit bill, fixing the code is important, since your audited payroll feeds the report that sets your next experience mod, which is the factor that moves your premium at renewal.
Frequently asked questions
How long after the policy ends can a workers comp audit happen?
Your insurer can audit during the policy period and for up to three years after it ends. Most audits happen within 90 days of expiration, but a carrier can come back later inside that window, so keep payroll records and subcontractor certificates at least that long.
Can a workers comp audit result in a refund?
Yes. Final premium is your actual payroll times the rates, and that math runs both directions. If your audited payroll lands under the estimate you paid, the carrier owes you money back, which is a good reason to finish the audit promptly in a year when the business shrank.
Do 1099 workers need workers comp coverage at audit?
Often yes, at least for premium purposes. An auditor will audit 1099 payments you made versus your state's employment tests. A 1099 (worker) is considered a payroll worker if they function like an employee, or if they are a subcontractor with no certificate on file. The tax form does not make that decision. It is based upon the way you work together and whether you have a certificate on file.
This guide is for educational purposes and summarizes standard NCCI policy language. Your policy's specific terms, conditions, and endorsements control. Talk to a licensed broker about your actual exposures.
The Bottom Line
A workers compensation audit will replace the initial premium you calculated for this year with what your actual payroll and job codes produced and by how much your uninsured subcontractor(s) added to that number. The surprises are preventable. Obtain a certificate from each subcontractor prior to starting the project, reconcile payroll with your 941s each quarter and have your broker adjust the premium estimate at the end of each contract year so there is as little adjustment in subsequent years.
References
- 1.California Legislature. “Insurance Code Section 11760.1.” Accessed July 2026. https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=INS§ionNum=11760.1. ↩
- 2.California Legislature. “Insurance Code Section 11737.” Accessed July 2026. https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=INS§ionNum=11737. ↩