Workers' Comp for Contractors: What Happens at a Workers' Comp Audit (and How to Avoid a Surprise Bill)

A workers’ comp audit is your insurer’s check, after the policy year ends, of what you actually paid in payroll and what kind of work it was for. Your premium was billed up front on an estimate; the audit replaces that estimate with real numbers, so you get either a refund or a bill.

Contractors get surprise audit bills for a handful of predictable reasons: subs without their own insurance, payroll put in the wrong class code, and no records to split a worker’s hours between codes. This guide explains how premiums are calculated, what happens during the audit, what to have ready, and how to keep the final number close to what you budgeted.

The core of the premium is payroll, broken out by class code, times each code’s rate per $100 of payroll, times your experience modifier:

Premium = (Payroll in each class ÷ 100) × Class rate × Experience mod

Credits, discounts, fees, and state assessments are added on top, but payroll and class codes drive most of the number. That is why the audit focuses on them.

A remodeler buys a policy based on estimated payroll. The rates below are examples; yours come from your state and insurer.

The extra field payroll was a growing business, which is fine. The $7,200 for the uninsured sub was avoidable with one certificate of insurance.

Every employee’s payroll goes into a class code that describes the work, and each code has its own rate. Most states use the classification system from NCCI (the National Council on Compensation Insurance). These codes come up most often for remodelers:

Code descriptions are from Tennessee’s list of NCCI contracting codes; the notes on 5437, 5606, 8810, and 8742 follow guidance from Missouri Employers Mutual. Rates differ by state and insurer.

Not every state uses NCCI codes. California, New York, New Jersey, Pennsylvania, and Delaware run their own classification systems, and Ohio, Washington, North Dakota, and Wyoming insure through state funds. Ask your agent which system applies to you.

Every workers’ comp policy is audited, usually soon after the policy year ends. The process is routine and follows the same steps with most insurers:

1. You get a notice. The insurer tells you which type of audit you have and what records to send.
2. The audit happens in one of three ways. A mail or online audit, where you fill in a form and upload records; a phone audit, where an auditor walks through your records with you; or a physical audit, where an auditor visits or meets you virtually. Larger and more complex policies usually get the more detailed audits.
3. The auditor reviews your records. They check total payroll, which class code each employee belongs in, payments to subcontractors and 1099 workers, and whether each sub had their own workers’ comp insurance.
4. The auditor calculates the actual premium. Real payroll, by class, replaces the estimate your premium was based on.
5. You get the result. An audit statement goes to you and your agent, followed by an additional premium bill, a credit, or no change.

The audit itself is not an accusation. It is the second half of how workers’ comp is priced: estimate first, actual numbers later. Sources: Nationwide, Harford Mutual.

Gather these before the audit date. When a record is missing, the auditor generally has to use the more expensive assumption.

• Payroll register for the policy period, by employee, with gross pay, overtime shown separately, and job title
• Quarterly federal payroll returns (Form 941) and state unemployment reports, to confirm totals
• Hours by type of work for anyone who works in more than one class code
• List of all subcontractors and 1099 workers with the total paid to each
• Certificates of insurance showing each sub’s workers’ comp coverage was active while they worked for you
• Subcontractor invoices, especially for any sub without a certificate
• General ledger or profit-and-loss statement for the policy period
• Job descriptions for office, sales, and supervisory staff you want placed in lower-rated codes
• Owner and officer details, including whether they are included in or excluded from coverage

Builders Mutual’s audit kit adds two practical tips: handwritten certificates are not accepted, and certificates should be collected again every quarter to catch policies that lapsed.

If you can’t show a certificate proving a sub had workers’ comp while working for you, insurers generally treat what you paid them as your payroll and charge premium on it, in the class code for the sub’s work. Most state laws also make you responsible if an uninsured sub’s worker gets hurt on your job. Collect a certificate before the first day of work.

Common mismatches: an office manager coded as clerical (8810) who also visits job sites, a cabinet installer coded as 5437 on a crew that also frames, or a superintendent coded 5606 without a layer of supervision between them and the crew. The auditor will move that payroll to the code that fits the actual work, often at a higher rate.

A worker who does work in two class codes can often have their payroll divided between them, but only if your records show the hours in each. Without those records, the auditor generally puts all of that worker’s payroll in the highest-rated code that applies.

In NCCI states, the extra half of time-and-a-half pay can usually be left out of workers’ comp payroll, but only if your payroll records show it separately by employee. Otherwise, the full overtime pay counts.

Rules on whether owners, partners, and corporate officers are covered, and how their pay is counted, vary by state and business type. Settle this with your agent when the policy is written, not at the audit.

Three of the five problems above are record problems, and they are solved during the year, not the week before the audit.

• Hours by type of work. If a worker clocks into a job and the kind of work they’re doing (carpentry, trim, supervision), you have the records to split their payroll between class codes.
• Overtime shown separately. Time records that feed payroll by week make it simple to show straight time and overtime premium as separate amounts.
• Approved hours, not reconstructed ones. Hours approved daily by the crew lead match payroll, and payroll matches your quarterly filings, which is the first thing an auditor checks.
• Sub records kept with the job. When each sub’s certificate and invoices are stored with the jobs they worked, pulling the year’s list takes minutes.

Our guide to time tracking for construction crews covers how to set up clock-ins by job and the daily approval routine.

Audit results can be corrected when the records support a change. Move quickly; insurers and states set time limits.

1. Read the audit statement line by line. Compare payroll by class code with your own records and look for subs charged as uninsured.
2. Ask for the auditor’s worksheets. Ask how each number was reached, especially any class code changes.
3. Send what was missing. A certificate of insurance, a job description, or records showing a payroll split can change the result. Ask whether late documents can be considered.
4. Bring in your agent. A good agent knows the classification rules and the insurer’s process for a review.
5. Request a formal review. Most insurers have a dispute or re-audit process. If that fails, many states let you appeal through the state insurance department or rating organization.

Pay any amount you don’t dispute on time. An unpaid audit bill can lead to cancellation, and working without coverage is a much bigger problem than a disputed invoice.

A clean audit starts with clean daily records. MotionOps keeps them for contractors whose jobs run for days or weeks:

• Field time tracking with GPS, by job, from each worker’s phone
• Approval workflows so hours are checked before payroll
• Timesheets and payroll prep from the same approved hours
• Expenses and receipts by job, including what you paid subcontractors
• HR document management for employee records

Try MotionOps free for 14 days and start building next year’s audit file today.