A workers' compensation premium audit reconciles the estimated payroll you were quoted on against what you actually paid during the policy year. The three findings that generate the largest additional premium bills are uninsured subcontractors whose payroll gets added to yours, payroll classified into the wrong class code, and undocumented overtime. Contractors who keep certificates of insurance for every subcontractor and separate payroll records by class code routinely avoid four- and five-figure audit bills. Actual audit outcomes depend on your carrier, state rules, and your records.
What a Premium Audit Actually Is
Workers' compensation premium is priced per $100 of payroll by class code. At the start of the policy year you provide an estimate; at the end, the carrier audits actual figures and reconciles the difference. If you overestimated, you may get a credit. If you underestimated, you get a bill.
The bill itself is not the problem. The problem is that most contractors never see it coming, because the largest audit findings usually have nothing to do with how much the business grew.
The Three Findings That Cost the Most
1. Uninsured subcontractors
This is the big one. When a subcontractor cannot produce a valid certificate of insurance covering the dates they worked for you, most carriers treat what you paid them as your payroll and charge premium on it at your rate.
Consider a contractor who paid $180,000 to subs over a policy year and cannot locate certificates for three of them totaling $60,000. At a class rate of $8 per $100 of payroll, that oversight is roughly $4,800 in additional premium. On a roofing class code it can be several times that.
The failure mode is almost never refusing to collect certificates. It is collecting one at the start of a long job and never getting the renewal when the sub's policy expired mid-project.
2. Payroll in the wrong class code
Class codes carry dramatically different rates. Clerical and estimating work is rated near the bottom; roofing and framing near the top. If your office manager who also does occasional field runs is classified entirely as field labor, you are paying the high rate on payroll that mostly belongs in a low-rated code.
Most states permit division of payroll between codes, but only when your records genuinely support the split at the time the work was performed. Reconstructing it after the audit rarely works.
3. Overtime not broken out
In many jurisdictions the premium portion of overtime can be excluded from audited payroll when it is separately recorded. If your books show only gross wages, the entire amount is typically included. For a contractor running heavy overtime through a busy season, breaking out that premium portion is meaningful money.
The Records to Have Ready
Assemble these before the auditor contacts you rather than after:
- Payroll registers, broken out by employee and class code
- Quarterly state and federal payroll tax filings
- A complete subcontractor list with certificates of insurance covering the exact dates worked, including renewals
- 1099 records
- General ledger or job cost reports
- Overtime records separated from base wages
- Records supporting any payroll division between class codes
Contractors who walk into an audit with this organized typically finish faster, with fewer findings, and with far more leverage if something needs to be disputed.
The Subcontractor Certificate Habit
If you take one operational change away from this article, make it this: no subcontractor starts work without a current certificate on file, and every certificate gets checked against the job's end date.
Set a calendar reminder for each sub's policy expiration on any job that will run past it. A renewal certificate takes them thirty seconds to request from their broker and saves you from paying premium on their payroll.
What to Do If the Bill Already Arrived
Audits can generally be reopened or appealed within a window that varies by carrier and state. The disputes that succeed are documentary. If you can locate certificates that existed at the time, produce payroll records showing proper classification, or demonstrate that clerical duties were rated as field labor, there is a real path to a revision.
Call your broker before you call the carrier. Part of what a broker does is advocate through exactly this process, and the framing of an audit dispute matters.
The Bottom Line
The premium audit is not a penalty. It is a reconciliation, and it is entirely predictable if you keep three habits: collect and renew subcontractor certificates, classify payroll accurately and document the split, and break out overtime in your books.
Contractors who do those three things rarely see a surprise. Contractors who do not tend to discover the cost at the worst possible time, months after the work has been billed and the cash has been spent.
Frequently Asked Questions
Why did I get a bill after my workers' comp policy expired?
Your premium was originally calculated on estimated payroll. The audit compares that estimate to actual payroll for the policy period and bills or credits the difference. If you grew during the year, hired more field staff, or used subcontractors who could not prove their own coverage, actual payroll exceeds the estimate and you owe the difference. This is normal and expected, though the size of the bill is often not.
Why is my subcontractor's payroll on my audit?
If a subcontractor cannot produce a valid certificate of insurance covering the period they worked for you, most carriers treat that subcontractor as your employee for premium purposes and charge you premium on what you paid them. This is the single largest source of surprise audit bills for contractors. The fix is collecting a certificate before the sub starts and keeping it on file through the audit, including renewal certificates if the job spans their policy expiration.
Can I dispute a workers' comp audit?
Yes. Audits can be appealed or reopened, typically within a defined window that varies by carrier and state. The realistic path to a successful dispute is documentation: certificates of insurance you did have, payroll records showing correct classification, and evidence of clerical or supervisory duties that were rated as field labor. Disputes based on records generally succeed; disputes based on disagreement with the rate generally do not.
How should I split payroll between class codes?
Most states allow payroll division between class codes when records clearly support it, but the rules are specific. Time spent must be genuinely separable and documented contemporaneously, not estimated after the fact. Clerical, estimating, and outside sales roles typically carry much lower rates than field labor. Without records, carriers generally apply the highest applicable rate to the entire payroll for that employee.
Does overtime count at full value in a workers' comp audit?
In many states the premium portion of overtime, meaning the extra half or full time above the base rate, can be excluded from audited payroll if it is separately recorded in your books. If overtime is lumped into gross wages without breakout, the full amount is generally included. Separating overtime in payroll records is one of the easier ways to reduce audited payroll legitimately.
What records should I have ready before the auditor arrives?
Payroll registers by employee and class code, quarterly state and federal tax filings, a subcontractor list with certificates of insurance covering the exact period worked, 1099 records, a general ledger or job cost report, and overtime records separated from base pay. Contractors who assemble these in advance typically complete audits faster and with fewer disputed findings.