How to Prepare for a Workers' Compensation Premium Audit

The short version

When a workers' compensation policy is written, nobody knows what your payroll will be for the coming year. The premium you pay during the policy term is a deposit calculated on an estimate. After the policy expires, the insurer audits your actual payroll, applies the classification rules to it, and issues a final premium. If you paid in more than the final figure you get money back; if less, you get a bill. That is the entire purpose of the audit, and it happens on every policy, every year.

For a plumbing company the audit has three pressure points. The first is classification: whether the auditor can verify the dual-wage split between 5183 and 5187 and the clerical and sales exceptions, covered in Workers' compensation payroll classifications for plumbing contractors. The second is subcontractors: anyone you paid for labor who cannot be shown to have had their own coverage is charged to your policy. The third is growth: a company that added two trucks mid-year will owe additional premium, and the time to plan for it is before the auditor calls.

A realistic scenario

A drain and sewer company in Fresno starts the policy year with eleven employees and an estimated payroll of $720,000. The year is better than expected. By spring it has hired three more technicians, and during a backlog in the summer it brings in two independent operators with their own jetting rigs for about $48,000 between them. The owner pays the two operators on 1099s and never asks for a certificate.

The audit request arrives six weeks after expiration. The office manager sends the payroll register and the 941s. Actual payroll is $905,000, so there is additional premium on $185,000 of plumbing payroll before anything else is considered. Then the auditor asks for the 1099s and the vendor ledger. One of the two operators had a workers' compensation policy and produces a certificate after the fact; the other was a sole proprietor with no employees and no policy. His $26,000 is added to the company's 5183 payroll. Finally, the register shows a single gross wage line per employee with no breakdown of overtime, so the premium portion of a busy summer's overtime, which could have been excluded, is charged in full.

The additional premium bill is substantial. About two-thirds of it was inevitable, the price of a good year. The other third, the uninsured operator and the undocumented overtime, was a records problem that cost real money and would have taken an hour to prevent.

Why audits happen

Final premium = audited payroll, by classification, multiplied by the rate for each classification, adjusted by the experience modification and any schedule credits or debits the policy carries.

Everything in that formula except the audited payroll was fixed when the policy was written. The audit supplies the missing input. The insurer has the right to examine your records under the policy's conditions, and the final premium has to be based on actual exposure, so neither you nor the carrier can agree to skip it.

Audits take two forms under the USRP. A physical audit is a review of your original payroll records; it does not have to be in person and is often done remotely, by phone and screen share or by uploading records. A voluntary audit relies on a payroll statement you sign. A policy with final premium of $10,500 or more must be physically audited at least once a year, and the last audit must be a physical audit of the full policy period. A smaller policy that reports payroll in the higher-wage half of a dual-wage construction classification (for plumbing, 5187) must also be physically audited unless it is a renewal and one of the two preceding policy periods was physically audited. Whatever the form, the information requested is the same.

What the auditor asks for

Have these ready for the exact policy period (not the calendar year, unless they coincide):

Two of these deserve a closer look.

Overtime

In California, only the straight-time portion of overtime counts as remuneration. The overtime excess (the increase above the regular hourly wage: the extra half-time in time-and-a-half, or the extra full-time in double-time) is excluded from the payroll on which premium is calculated. In practice the auditor can only exclude what the payroll records show separately, and how a guaranteed-wage or salaried arrangement is treated is worth asking your insurer about in advance. A register that shows a blended gross figure gives the auditor nothing to exclude. Most payroll services can produce the breakdown; the setting has to be turned on and the report has to be run.

Subcontractors

The auditor's job here is to find labor you paid for that was not on your payroll and decide whether it should be charged to your policy. The vendor ledger and 1099s are the trail. For each payee, the question is whether they were an independent business with their own workers' compensation coverage, and the proof is a certificate of insurance showing a policy in force for the period you paid them.

Without a certificate, the subcontractor's labor cost is treated as your payroll and charged at the rate for the trade the subcontractor performed. How an insurer values that labor when the subcontractor's own payroll records are not available, and how it treats a contract that combines labor and materials, are questions to ask before you hire the subcontractor, not after the audit. A certificate obtained after the fact, as in the Fresno scenario, generally works if it shows the policy was in force during the period; a sole proprietor with no employees and no policy has nothing to produce.

There is a separate licensing dimension to this. In California, under Labor Code section 2750.5, a person performing work that requires a contractor's license and does not hold one generally cannot be treated as an independent contractor, and the workers of an unlicensed subcontractor are in practice treated as the hiring contractor's employees for workers' compensation. That means paying an unlicensed helper on a 1099 does not make them a subcontractor in the auditor's eyes. Are plumbing subcontractors covered by your insurance? covers the coverage side of that question.

The audit timeline

A typical sequence, with the caveat that each insurer runs its own process:

1. Policy expires. Your deposit premium has been paid through the term.
2. Audit notice arrives, usually within a few weeks to a few months of expiration, asking for records or scheduling a visit.
3. You provide records. Most insurers give a response window; asking for a short extension in writing is normal and almost always granted.
4. The auditor prepares the audit worksheet showing payroll by classification, subcontractor charges, exclusions taken, and the resulting final premium.
5. The insurer issues an audit statement with either a return premium or an additional premium invoice, payable by the due date on the invoice.
6. Audited payroll is reported to WCIRB on the unit statistical report, where it becomes the expected-losses side of your X-Mod for three consecutive ratings. Because the policy year you are renewing is excluded from the experience period, those three ratings start with the second renewal after the audited policy began, not the next one.

Step six is the one plumbing owners tend to overlook. The audit does not just settle last year's bill; it fixes the payroll data that sits in your mod for three ratings. How to read a California workers' compensation experience rating worksheet shows where it lands.

When the audit is wrong

Audits contain errors in both directions, and the policyholder is the only party with the records to find them. Read the audit worksheet rather than just the invoice. The common problems:

• Payroll in the wrong classification: a clerical employee in 5183, a plumber above the threshold in 5183 because the time records were not provided, an estimator in the plumbing code.
• Subcontractors charged when a certificate exists but was not sent.
• Overtime charged in full when the breakdown exists but was not run.
• Period errors: payroll from before inception or after expiration included, or a pay period counted twice.
• Owner or officer payroll charged when an exclusion was on file, or charged above the maximum.

To dispute, write to the insurer's premium audit department. Identify each line, state the correct treatment, and attach the record that proves it. Keep it factual; the auditor can only change what the records support. If the insurer declines to revise and you believe the classification or rating rules were misapplied, Insurance Code section 11737 provides a formal path. You file a written Complaint and Request for Action with the insurer or WCIRB. If that is rejected, you can appeal to the Department of Insurance's Administrative Hearing Bureau, generally within 30 days of the written decision (with longer windows if no decision is issued). Ask the insurer in writing how it handles the disputed amount while the complaint is pending.

An additional premium invoice is a debt under the policy. Unpaid audit balances can be referred to collections, and applications commonly ask about outstanding premium. Paying the undisputed portion while disputing the rest, in writing, keeps the account in good standing without conceding the point.

Practical takeaway

1. Treat the audit as a scheduled event. Put the expiration date and a 60-days-after reminder on the calendar and assign one person to own it.
2. Build the file during the year, not after it. A folder with each quarter's 941 and DE 9, the payroll register with overtime split out, and a certificate for every subcontractor you have paid means the audit is a day's work instead of a month's.
3. Collect certificates before the first check. Make a current workers' compensation certificate a condition of paying any subcontractor, and diary its expiration.
4. Keep original time records for everyone in the field, with daily start and end times, and keep them for salaried plumbers too. The dual-wage split lives or dies on it.
5. Estimate accurately at inception and tell the broker mid-year when payroll is running well ahead. A mid-term endorsement spreads the increase instead of concentrating it in one invoice.
6. Review the worksheet, not just the bill, and dispute in writing with documents.

For the Fresno company, the inevitable part of the audit was the cost of a good year, and the owner could have spread it by updating the payroll estimate in the spring. The avoidable part was one missing certificate and one payroll report setting. Both are now on the checklist for next year.

If you have an audit notice in hand and are not sure what to send, or an audit bill you think is wrong, ask a licensed producer before the response deadline. The records that answer the auditor's questions are usually already in your payroll system; the work is knowing which reports to run.