Bookkeeping · Payroll & Compliance · Brief · Intro level
Workers' comp for bookkeepers: premiums, the audit, and the true-up entry
How workers' compensation premiums are priced off payroll by class code, why the annual audit produces a bill or a refund, and how to book the adjustment.
Workers' compensation is the insurance priced off your payroll ledger. The carrier charges a rate per $100 of payroll, by job classification code, adjusted by an experience modifier for claims history — then trues the whole thing up after year-end by auditing your actual books. For the bookkeeper that means three jobs: keep payroll separable by class, keep subcontractor certificates on file, and book the audit adjustment when it lands.
How the premium is built
Coverage is state-regulated (a few states run monopolistic state funds), but the pricing skeleton is consistent. Each job type carries a class code and a rate reflecting its injury risk — clerical is cheap, roofing is not:
Illustrative only; actual rates vary widely by state, carrier, class code, and experience modifier.
The experience modifier scales the whole premium up or down based on claims history versus similar businesses — a mod above 1.0 means claims are costing you at renewal, not just at the deductible. Because rates differ this much by class, payroll coding is money: an office manager misclassified into the shop-floor class can multiply that person's premium several times over. Keep wages by employee and class separable in the payroll system, and split-duty employees documented, since carriers only honor payroll splits backed by records.
The audit
Within a few months after the policy year ends, the carrier audits: a questionnaire, a call, or a visit. The auditor asks for payroll registers, the quarterly Forms 941, state unemployment reports, and the general ledger — then recomputes premium on actual payroll versus the estimate the policy was priced on.
Two audit rules do most of the damage:
- Uninsured subcontractors count as payroll. Payments to subs without their own coverage get charged premium as if the subs were your employees. A current certificate of insurance for the period worked is what removes them — the file described in /bookkeeping/payroll-compliance/contractor-file-checklist.
- Everything defaults to the highest class when records can't support a split. Undocumented is expensive.
Definitions of audit "payroll" (overtime premium portions, tips, certain fringes) vary by state rulebook — answer from the carrier's worksheet definitions, not assumptions.
Booking the true-up
| Account | Debit | Credit |
|---|---|---|
| Workers' comp insurance expense | 1,850 | |
| Accounts payable | 1,850 |
A return premium reverses the entry: debit cash or receivable, credit the expense.
Book the adjustment when the audit resolves. If the business accrues comp monthly against estimated payroll, compare accrual to audited actuals annually and tune the rate you accrue at — a policy that trues up big in the same direction every year is being estimated wrong.
The maintenance routine
- Verify class codes on the policy against what people actually do, at every renewal and every new role.
- Collect and diary COIs from every subcontractor before they start.
- Reconcile the payroll the auditor will see (941s, SUI reports) to the ledger quarterly so the audit holds no surprises — the same tie-outs described in /bookkeeping/payroll-compliance/form-941-basics.
- When entering a new state, confirm coverage extends there before the first hire (/bookkeeping/payroll-compliance/state-payroll-registrations).
Frequently asked questions
- How are workers' compensation premiums calculated?
- Premium is generally a rate per $100 of payroll, set by job classification code, multiplied by an experience modifier reflecting the employer's claims history. The policy starts with estimated annual payroll; after the policy year ends, the carrier audits actual payroll and bills or refunds the difference.
- What is a workers' comp audit?
- An annual review — by questionnaire, phone, or visit — in which the carrier verifies actual payroll by class code for the expired policy year. The auditor works from payroll reports, 941s, and the ledger, and will charge premium on payments to uninsured subcontractors unless certificates of insurance are on file.
- How do I book a workers' comp audit adjustment?
- An additional premium bill is a debit to workers' comp insurance expense and a credit to cash or accounts payable; a return premium is the reverse — cash or receivable debited, expense credited. Book the adjustment in the current period when the audit resolves, and flag unusually large ones for the tax preparer.