Construction accounted for around 16% of all company insolvencies in England and Wales in the twelve months to May 2026, a higher share than any other sector, against a base of roughly 14% of all registered UK businesses according to BCIS. Very few of those businesses ran out of work. They ran out of cash or found out too late that the margin they had been reporting was never really there.
Overbilling and underbilling in construction sit close to the centre of that problem. Most finance and commercial teams meet the terms in a WIP schedule rather than a textbook. One column reads billings in excess of costs and earnings. Another reads costs and earnings in excess of billings. Both move month to month, usually for reasons nobody can fully explain in the room.
Whether that movement matters depends on what's driving it. Sometimes it's contractual timing and entirely benign. Sometimes it's the first visible symptom of a project that has already drifted, and the WIP report is simply the only place it has surfaced so far.
What Overbilling and Underbilling in Construction Actually Mean
Both describe the same gap measured in opposite directions: the distance between what you have billed a client and what you have actually earned by completing work.
Overbilling: billed ahead of the work
You have raised applications and been certified for more than the value of work performed to date. Cash arrives early. Under IFRS 15, this sits on the balance sheet as a contract liability, because you are carrying an obligation to deliver work the client has already paid for. ACCA's technical guidance on contract assets and liabilities sets out the treatment clearly for anyone who needs the accounting reference.
Underbilling: work ahead of the billing
Work has been done, costs are in the ledger and revenue has been earned, but the corresponding application either hasn't been raised or hasn't been certified. That's a contract asset. In simple words, unbilled revenue, with the cash sitting in the client's account rather than yours.
The distinction between overbilling vs underbilling in construction is simple enough on paper. What makes it difficult in practice is that neither figure means anything unless the cost side is complete. An underbilled position calculated from partial cost data isn't underbilling at all. It's a reporting artefact, and it will reverse the moment the missing invoices land.
Why the Imbalance Appears In the First Place
Front-loaded valuations are the obvious cause, and often perfectly legitimate. Mobilisation, temporary works, site establishment and early procurement all consume cash long before there's much visible progress on site, so payment schedules get weighted forward by agreement. That's a commercial decision, not an accounting failure.
The unintentional causes are the ones worth watching.
- Cut-off dates that don't line up. The valuation is measured to the 20th. The cost ledger closes at month end. Ten days of subcontractor work and material deliveries sit outside the comparison entirely. On a project turning over £2 million a month, that gap on its own can move the reported position by six figures.
- Variations that haven't been priced. Under NEC or JCT, instructed work regularly gets built well before it's valued. Costs land in the ledger, the value doesn't follow, and the project reads as underbilled when what's actually happening is unrecovered change. The cost of delayed change recognition is well documented and it lands here first.
- Committed costs that haven't reached finance. A purchase order is a commitment the moment it's raised. In a cost report built from posted invoices, it doesn't exist yet. Procurement and finance running on different timelines is one of the most common reasons a billing position looks healthier than it is.
- Subcontract certification lag. A subcontractor submits a payment application late, or the QS certifies after the finance cut-off, and a month of cost quietly disappears from the comparison.
- Costs that never get coded properly. Plant left on hire past its return date. Agency labour booked to the wrong cost code. Materials delivered to site with no goods received note against them.
Most contractors don't notice any of this on a single project. It shows up when you consolidate twenty of them and the group WIP position swings by more than the month's profit.
Why Neither Position is Automatically Good or Bad
Overbilling tends to get treated as the responsible one and underbilling as the sloppy one. That reading is too simple.
A steadily overbilled project can be a well-run job with a sensibly negotiated payment schedule. It can equally be a job where the commercial team has claimed hard to protect cash while the cost position deteriorates underneath. In the WIP column, both look the same.
Underbilling can mean a genuine administrative backlog. It can also mean a commercial team that has quietly stopped submitting variations because the client keeps rejecting them, which is a contractual problem months before it becomes a billing one.
The position on its own tells you very little. The trend, and the reason behind the trend, tell you almost everything.
How Overbilling and Underbilling in Construction Affect the Financials
Cash flow
The impact of overbilling on construction cash flow is the reason so many businesses run this way deliberately. An overbilled portfolio funds its own working capital, reduces reliance on facilities and makes the monthly cash position look comfortable.
The catch is that the cash is borrowed from your own future revenue. As a project approaches completion, billing has nowhere left to run while costs continue to land, and the position unwinds. Cash tightens sharply in the closing months of a job that felt healthy for two years. Finance teams forecasting from historic receipts rather than from the billing curve get caught by this every time.
Underbilling does the opposite. You've paid your supply chain, paid your labour and funded the materials, and the client is holding the money. On a business with £40 million of turnover, a persistent underbilled position of even 2% is £800,000 of working capital sitting somewhere other than your bank account.
Revenue recognition
Revenue recognised over time depends on percentage of completion, and percentage of completion depends on cost incurred measured against a current forecast cost-to-complete. If the cost-to-complete hasn't been revisited since the last commercial review, the percentage is wrong and the revenue figure inherits that error.
This is where revenue recognition and overbilling in construction become genuinely dangerous rather than merely untidy. Revenue is being recognised against progress that hasn't been independently verified, in a period where the billing position suggests everything is fine.
Profitability
Neither position changes the final profit on a contract. Both change how profit appears in the period.
The most damaging combination is overbilling alongside incomplete cost capture. Revenue is recognised in full, costs are recognised partially, and the margin looks strong for two or three periods before correcting hard. Most commercial directors have seen at least one version of the job that was comfortably ahead at 60% complete and lost money by handover.
WIP reporting
A WIP schedule is only as reliable as the cost-to-complete sitting underneath it. Construction WIP overbilling and underbilling analysis carried out on stale forecasts produces confident numbers built on assumptions that stopped being true weeks ago.
Auditors know this, which is why WIP is one of the first areas they test and why year-end adjustments in construction so often cluster around these two columns.
Forecast accuracy
Every forward-looking number in the business, cash forecast, margin forecast, covenant headroom, group P&L, is built on the same underlying project data. A billing position that lags reality passes that lag straight into the forecasting dashboards leadership uses to make decisions.
Warning Signs Worth Checking Before the Next Board Pack
- The overbilled position on a project keeps growing after the halfway point, when the billing curve should be flattening.
- Underbilling is concentrated on the contracts with the highest variation volume.
- The WIP position shifts materially between the draft and the final CVR.
- Cost to complete on a live project hasn't moved for two consecutive periods.
- Reported gross margin on a project moves by more than a point or so with no identified cause.
- Retention and advance recovery are being tracked in a separate spreadsheet from the main cost report.
One of these on its own is a conversation. Three of them on the same project usually means the commercial position and the accounting position have separated, and somebody will be reconciling them by hand at year end.
How Integrated Project Controls Reduce the Risk
The root problem isn't billing discipline. Most QS teams are perfectly disciplined. The problem is that the information needed to judge a billing position properly is scattered across a procurement system, a subcontract register, a cost ledger, a valuation spreadsheet and somebody's inbox, and each of those sources updates on a different clock.
Project financial controls in construction work when those inputs land in one place at the moment they happen rather than at month end.
Commitments recorded when they're made
When a purchase order registers as committed cost immediately, the cost side of the comparison stops being a lagging indicator. Committed spend against budget becomes visible at package level while there's still time to act on it, which is the difference between job cost accounting that reports history and job costing that surfaces exposure.
Variations handled as commercial events
Instructed change needs to carry its cost and its value from the point of instruction, not from the point somebody remembers to price it. Once variations sit inside the same commercial workflow as the base contract, the gap between work done and work claimed narrows on its own.
Subcontract certification inside the same system
Applications, certifications, retention and advance recovery belong in the same record as the subcontract they relate to. When certification happens in the system rather than alongside it, the cost position at cut-off reflects what has actually been certified rather than what somebody has had time to key in.
A CVR that produces the WIP posting
This is the one that matters most. When the cost value reconciliation is frozen for the period and that freeze generates the WIP journal directly, the commercial position and the accounting position can't drift apart. There is no second version of the truth for anybody to reconcile later.
How to prevent overbilling in construction and how to reduce underbilling turn out to be the same discipline described from two angles: close the gap between when something happens on site and when it becomes visible in the numbers. Most construction billing best practices are downstream of that one principle.
How Xpedeon keeps the CVR and the WIP posting in step
Xpedeon is a construction ERP rather than a WIP reporting layer sitting on top of a general ledger. Procurement commitments, subcontract certifications, valuations and payroll all post against the same project data, and the CVR period freeze triggers the WIP journal into the general ledger without a manual rebuild.
That's the mechanism. The results clients report tend to be about time and visibility rather than accounting elegance.
Lovell Partnerships reduced its subcontractor payment cycle from four days to 1.5 and described a tenfold improvement in commercial visibility after moving off disconnected spreadsheets and point systems.
Sobha Group cut invoicing time by 60% once validation workflows stopped running through manual reconciliation.
For a wider view of how these pieces connect, the construction accounting software guide covers the full picture from job costing through to financial close.
If your WIP position is being rebuilt in a spreadsheet every month and nobody is entirely confident in the answer, Book a Discovery Call and we'll walk through what the alternative looks like on your contracts.