Workers Comp Payment Options for California Contractors: Pay-As-You-Go vs Monthly Installments

Every California contractor with employees pays workers comp — but how you pay it is a choice most contractors don't know they have. The traditional route is a deposit plus monthly installments calculated from an estimate of your annual payroll, squared up at a year-end audit. The alternative is pay-as-you-go (often written PayGo), where the carrier pulls your actual payroll from each pay run and bills premium against the real number. Same coverage, same WCIRB class codes, same X-Mod — very different cash flow, and a very different audit experience. This guide walks through both structures and what the annual premium audit looks like under each.

How Workers Comp Premium Is Actually Calculated

Whichever payment structure you choose, the premium formula is the same. California workers comp is rated per $100 of payroll, by WCIRB classification code, adjusted by your experience modification factor:

(Rate per $100 × Payroll ÷ 100) × X-Mod = Premium

A framing crew on class 5403 at $18 per $100 with $400,000 of payroll and a 1.0 X-Mod generates $72,000 in annual premium. The payment structure doesn't change that number — it changes when you pay it and how accurate the number is before the audit reconciles it.

The key variable is payroll. Under installment billing, the payroll number in that formula is a projection you and your broker set at the start of the policy year. Under pay-as-you-go, it's your actual wages, reported every pay period. Everything else about the two models follows from that one difference.

Option 1: Traditional Monthly Installments

The classic structure works like this: at binding, you estimate your annual payroll by class code. The carrier calculates an estimated annual premium, collects a deposit — commonly 15–25% — and spreads the balance over monthly or quarterly installments. Your payments are fixed and predictable all year, regardless of what your payroll actually does.

Where it works well: contractors with stable, predictable payroll. If you run the same four-person crew year-round and your payroll lands within a few percent of the estimate, installments are simple and the audit adjustment is small.

Where it hurts:

• The deposit ties up cash. A $60,000 estimated premium can mean $9,000–$15,000 due at binding — money that isn't available for materials, payroll, or equipment.
• Overestimate and you've made an interest-free loan to the carrier. You'll get the overpayment back after the audit — months after the policy year ends.
• Underestimate and the audit bill arrives all at once. If actual payroll came in 30% over estimate, roughly 30% of your annual premium lands as a single invoice, typically due in full within weeks of the audit.

Option 2: Pay-As-You-Go (Payroll-Linked Billing)

Pay-as-you-go connects your workers comp policy to your payroll system. The sequence looks like this:

1. Your broker places the policy with a carrier that supports PayGo billing.
2. PayGo billing is elected at issuance, usually with little or no deposit.
3. Your payroll provider transmits actual wages by class code automatically after each pay run.
4. The carrier calculates that period's premium against real wages and debits it via ACH.
5. At year end, the audit verifies what was already reported — adjustments are usually minor.

Integrations exist for the major payroll platforms California contractors actually use — Paychex, ADP, Gusto, QuickBooks Payroll, Rippling, OnPay, Square Payroll, and others. If you run payroll in-house or through a small local service, self-reported PayGo (you report wages each period through a carrier portal) is often available too.

Where it works well:

• Seasonal contractors. Premium falls with payroll in slow months instead of remaining fixed against a full-year estimate.
• Growing contractors. New hires flow into billing automatically — no mid-term endorsement lag, no year-end shock from headcount you added in month three.
• Cash-flow-sensitive operations. Little to no deposit, and premium tracks revenue-producing labor almost in real time.

The trade-offs are modest but real: your payroll data must be clean and class-coded correctly every period, ACH pulls happen every pay cycle (weekly payroll means weekly premium debits), and not every carrier offers PayGo on every class code — high-hazard trades may see fewer participating markets.

Side by Side

	Monthly Installments	Pay-As-You-Go
Premium basis	Estimated annual payroll	Actual payroll each pay run
Up-front deposit	Commonly 15–25% of estimated premium	Minimal, often none
Payment amount	Fixed all year	Rises and falls with payroll
Audit exposure	Full gap between estimate and actual	Small true-up in most years
Best fit	Stable year-round payroll	Seasonal, growing, or variable payroll

The Audit Under Monthly Installments

Every California workers comp policy is subject to a premium audit after the policy year ends — it's in the policy contract, and carriers exercise it. Under installment billing, the audit is where the estimate meets reality.

The auditor reviews your payroll records, quarterly DE 9/DE 9C filings, and general ledger, re-tallies actual payroll by class code, and recalculates the premium. Three outcomes:

• Actual ≈ estimate: small adjustment either way. This is the quiet outcome installment billing is designed for.
• Actual > estimate: an additional premium invoice for the difference. For a contractor who estimated $500,000 in payroll and ran $700,000 during a busy year, the audit bill on a $15-per-$100 class code with a 1.0 X-Mod is roughly $30,000 — due at once, arriving months after the wages were paid.
• Actual < estimate: a return premium — a refund of money the carrier held all year.

Unpaid audit balances are serious: carriers can cancel the renewal, report the balance, and other carriers may refuse to quote until it's resolved. The five-figure surprise audit bill is one of the most common cash-flow emergencies we see referenced by California contractors — and it is almost always an estimating problem, not a rate problem.

The Audit Under Pay-As-You-Go

PayGo policies get audited too — same contractual right, same records request. The difference is what the audit finds. Because premium was calculated from actual reported wages all year, the audit is mostly verification rather than reconciliation:

• Were wages classified to the correct WCIRB class codes?
• Was overtime handled correctly? (In California, the premium portion of overtime — the "excess" over straight-time — is generally deductible from auditable payroll when your records break it out.)
• Did you pay any uninsured subcontractors the auditor will treat as employees? Subs without their own workers comp certificates get picked up as payroll on your audit — under either billing model.
• Are owners and officers properly included or excluded, and at the correct WCIRB minimum/maximum payroll amounts?

When those items are clean, a PayGo audit typically closes with little or no adjustment, because there's no estimate gap to reconcile. PayGo doesn't make the audit go away — it makes the audit boring. For most contractors, that's exactly the goal.

What Auditors Look At Under Either Model

Payment structure changes the size of the true-up, not the scope of the audit. Either way, keep these clean throughout the year:

• Class code assignment by employee — misclassification is the most expensive audit finding. Dual-wage class codes (electrical 5190/5140, plumbing 5183/5187 splits, roofing 5552/5553 distinctions) hinge on documented hourly wages.
• Certificates of insurance for every subcontractor — collect them before the sub starts, keep them current, and verify workers comp specifically.
• Overtime records that separate straight-time from premium pay.
• Officer/owner elections — inclusion and exclusion forms on file and consistent with how payroll reports them.
• Separation of payroll on wrap-up projects — if you work OCIP/CCIP jobs, wrap payroll must be segregated so it isn't charged to your practice policy. See our wrap-up insurance guide.

A Common Misconception: PayGo Doesn't Mean Buying From Your Payroll Company

Payroll companies market pay-as-you-go workers comp aggressively, and many contractors assume the billing feature and the insurance have to come from the same vendor. They don't. PayGo is a billing method, not a product — independent brokers place PayGo policies with multiple carriers that integrate with whatever payroll platform you already run.

Why that distinction matters:

• Market access. A payroll-bundled program typically quotes one or two captive carriers. A broker can shop your class codes across many markets and still deliver PayGo billing on the winning quote.
• Class-code advocacy. Whether your crew is rated 5403 or 5645, or your electricians qualify for the high-wage class, is worth real money — and it's a broker conversation, not a payroll-company one.
• X-Mod review. Your experience modification factor should be checked annually for errors in reported losses and payroll. Payroll vendors don't do this.
• One relationship for the whole program. GL, auto, umbrella, bonds, and workers comp coordinated together — with consolidated certificates when a GC asks for proof of everything at once.

Which Payment Option Should You Choose?

• Seasonal payroll (roofing, painting, exterior trades): pay-as-you-go, almost always. Paying estimate-based installments through a slow winter is the worst version of the traditional model.
• Growing headcount: pay-as-you-go. Growth is what turns a reasonable estimate into a five-figure audit bill.
• Stable, predictable payroll: either works. If you like a fixed monthly number for budgeting, installments are fine — just review the payroll estimate with your broker mid-term if anything changes.
• Very small or owner-only operations: installments on a small premium are simple, and some PayGo minimums may not be worth it. Ask for both quotes and compare.

One more practical note: you can switch payroll providers mid-year on a PayGo policy — the integration gets re-linked without affecting coverage. And electing PayGo generally carries no premium surcharge; the rates and X-Mod are the same either way.

Getting Set Up

If you want payroll-linked billing, tell your broker at quoting time — carrier appetite for PayGo varies by class code, and it's easiest to elect at issuance. Bring your payroll platform name, your class codes, and last year's actual payroll by class. If you're mid-policy on installments and your payroll has moved materially from the estimate, ask your broker for a mid-term payroll endorsement now — adjusting the estimate today beats financing a surprise at audit.