The WIP Schedule, Explained: What Overbilling and Underbilling Are Actually Telling You

Every quarter, somewhere in a surety office and a bank credit department, someone opens your work-in-progress schedule and forms a judgment about whether your company tells itself the truth. Bonding capacity, line-of-credit renewals, and prequalification decisions all lean on this one report — because percentage-of-completion accounting is where a contractor's claimed profitability meets its actual job performance, line by line.

Inside most sub shops, though, the WIP is produced for those outsiders and barely read by insiders. That's backwards. The WIP is the best early-warning instrument the business owns: it surfaces margin fade while there's still schedule left to respond, exposes billing discipline problems while they're collectible, and reconciles the cash forecast with the P&L's story. Leaders who can't read their own WIP are flying on instruments they've never learned.

For each open job, the WIP holds five core numbers: contract value (base plus approved changes), estimated total cost, cost incurred to date, billed to date, and the derived pair that drives everything — percent complete (cost to date ÷ estimated total cost) and earned revenue (percent complete × contract value). Compare earned revenue to billed revenue and every job lands in one of two states: billed ahead of earnings (overbilled) or earned ahead of billings (underbilled).

Everything interesting about the WIP lives in why those gaps exist. The mechanical answer — billing timing — is the boring case. The important cases are the ones where the gap is a symptom: an estimate that's wrong, a change order that's unbilled, a schedule of values that front-loaded itself into a problem, or a loss nobody has admitted to the ledger yet. Reading the WIP means interrogating gaps, not just computing them.

Modest overbilling is healthy — it means your billing discipline front-runs your cost curve, and it's the cheapest working capital a sub can get. But every overbilled dollar is borrowed, not earned: you've collected for work you haven't performed, and the remaining work must be completed with money you've already spent. The liability line accountants call 'billings in excess' is exactly that — a liability.

The danger pattern is systemic overbilling funding operations: new jobs' front-loaded billings quietly covering old jobs' completion costs, which works precisely as long as new work keeps arriving. When backlog dips, the pyramid unwinds — the industry's oldest failure sequence, and one reason trust fund states criminalize using one project's money on another. The tell is company-wide: total overbillings growing quarter over quarter while margins fade. Your surety runs that exact screen; run it on yourself first.

Underbilling — cost incurred ahead of billings — always has a story, and only one of the stories is fine. The fine one: timing, a big month of cost right before the billing cycle, self-correcting within a cycle. The common one: unbilled change work — the field performed changes that were never captured, priced, and pushed to a signed CO, so the WIP shows you financing the GC's scope growth interest-free. With change orders running 8-14% of contract value on typical projects, a persistent underbill is often your margin sitting in an unsigned pile.

The grim story: the estimate is wrong, cost-to-complete is understated, 'percent complete' is inflated — and the underbilling is actually an unrecognized loss. Auditors probe exactly this, which is why chronic underbillings make sureties nervous far faster than overbillings do. The discipline that sorts the stories is the cost-to-complete review: PMs re-estimating remaining cost monthly, defended in a room, not rolled forward by habit. A WIP built on stale cost-to-completes isn't conservative or aggressive. It's fiction with columns.

Track each job's projected final margin across its life — bid margin, then the re-estimate each month — and you get the fade curve, the WIP's sharpest diagnostic. One job fading is a project problem. A portfolio that reliably bids at 8% and finishes at 3% is a company problem: estimating that misses the same categories repeatedly, field production that can't hit the recipe, unpriced contract risk surfacing as 'unforeseen' costs, or change work performed at arbitrary markups that under-recover. With industry average margins around a lean 3.1%, a two-point fade isn't erosion — it's the whole profit.

Fade analysis is also where the WIP meets the rest of your operating system: the estimating-to-field handoff determines whether the field ever knew the recipe; daily reports determine whether the causes of fade are documented or folklore; and the bid/no-bid log tells you which customers' jobs fade every time. Sureties read fade as the integrity of your estimating. So should you.

The WIP creates value in a meeting, not a PDF. Monthly, controller in the chair, PMs defending their jobs: cost-to-complete re-affirmed or revised with reasons; every underbilled job explained — timing, unbilled COs (with the list attached), or re-estimate; every overbilled job checked against remaining cost; fade flagged the month it appears, while there's still project left to respond. The rules are cultural as much as financial: bad news early is rewarded, rolled-forward estimates are challenged, and 'we'll make it up in the field' is not a line item.

Then connect the WIP outward. Feed the billing gaps to the 13-week cash forecast — an underbilled job is a receipts problem eight weeks from now. Feed the fade analysis back to estimating as calibration data. And give your surety and banker the same clean story you gave yourself: contractors who narrate their own WIP variances credibly get the benefit of the doubt — and the capacity — that silent ones don't.

The WIP schedule is your company's lie detector: it compares what estimating promised, what the field produced, what accounting billed, and what leadership believes, and it prints the disagreements. Overbilling is borrowed cash — fine until it's structural. Underbilling is either sloppy billing, unsigned change orders, or unadmitted losses — and finding out which is the controller's highest-value hour each month.

Read it like the people who judge you by it: fade first, gaps second, cost-to-complete integrity always. A sub whose leadership runs the WIP meeting with discipline gets truer estimates, faster billing, earlier warnings, and — not incidentally — the confidence of every surety and banker who's learned that the WIP is where contractors either face reality monthly or meet it all at once.

If your shop has never run a real WIP discipline, start smaller than the textbook: this month, just re-estimate cost-to-complete on your five largest jobs with the PMs in the room, and compare each job's current projected margin to its bid margin. That single exercise — two hours, no new software — usually surfaces the year's most important conversation, and it builds the muscle the full monthly meeting will need.