What’s Really Important in Construction?
Every contractor knows where the job is. Fewer know where the money is.
Walk onto any site in the country and ask the Site Manager how the job is going and you’ll get a straight answer, usually within seconds. Where they are against programme. Which trade held them up. What’s landing on site on Thursday.
Now ask the same question about the profit margin on that contract up to today, not at final account — and that answer is at best vague.
That gap, between what site knows and what the accounts show, is where margin quietly disappears. It isn’t bad workmanship or a thin order book. It’s that the numbers arrive too late, and in the wrong shape, to change anything. By the time the job’s costed properly it’s finished, and the chance to protect your margin has gone.
Busy is not the same as profitable
It’s one of the hardest lessons in this sector. Order book full. Three sites running. Everyone flat out. And yet the bank balance never quite reflects the effort.
💡 It happens more often in construction than anywhere else: your money doesn’t sit in the bank, it’s sitting out there on site.
It’s in work you’ve done but haven’t yet invoiced or applied for. In applications submitted but not yet certified or paid. In variations you carried out on a nod and never got signed off. In materials sitting on site, and in retentions — all the work and money you’ve already earned, held for months and sometimes longer after practical completion.
Meanwhile your subcontractors want paying, your merchants want paying, and your payroll run doesn’t wait for a certificate.
⚠️ You can be highly profitable on paper and still be unable to pay the wages and the subbies at the end of the week.
Growth often makes it worse, not better — every new contract needs labour, plant and materials funded before a penny of it is certified. It’s why construction records more company failures than any other sector in the UK: in the twelve months to June 2026 there were 3,805 construction insolvencies, around 17% of all cases. They run out of cash.
Those who thrive are the ones that know, in real time, exactly how much cash is tied up at each stage of each contract, how long it stays there, and exactly when they’ll get paid.
What are the numbers that matter?
Every business has a handful of drivers — the few numbers you can genuinely influence, measure and improve. Focus on those and you stop reacting to what’s happened and start controlling what’s next.
For contractors:
✅ Margin by contract, monthly. Not the margin you tendered, but what the job is actually earning right now. Your overall business figures can hide problems. One loss-making job can wipe out the profit from three good ones, so look at each job separately — what it’s actually making after its costs, not the profit you expected when you quoted.
✅ Cost to complete. Your accounts show what you’ve already spent. The harder question is how much you still need to spend to finish. Get that estimate wrong and a job can look profitable when it’s heading for a loss. Simply carrying forward last month’s estimate hides growing problems. Someone senior, who understands the job, should review and challenge the remaining costs every month.
✅ Work in progress, and over or under-billing. You need to know how much work you’ve actually done. If you’ve done the work but haven’t invoiced, that’s cost you’re funding yourself. If the client has paid in advance, you need to know how much of that money is still needed to finish the job.
✅ Variations and change control. When a client asks for a change, get written agreement on what you’ll do and what you’ll charge before starting. Otherwise you spend on labour and materials, the client disputes the bill, and it becomes work that cost you money and may never be invoiced. Every unsigned variation is an argument you’re going to have later, from a weaker position, with the money already spent — instead of an opportunity for more sales and profit.
✅ Retention. Somewhere between three and five per cent of your turnover is held by other people, released against dates most contractors don’t know, for fixing defects. Knowing the money is owed isn’t enough: you need an amount, a due date, and someone chasing it.
✅ Application-to-cash days. Don’t just measure debtor days — that understates how long it really takes to get paid. Measure the whole process: application submitted, certificate issued, payment received. The gap between what your contract says and what actually happens is your real funding requirement.
✅ Labour recovery. Compare the hours you pay your team for with the hours you allowed in your job prices. Travel, waiting for drawings, bad weather and going back to fix mistakes all cost money you can’t charge on. Leave those out of your job reports and the work looks more profitable than it is, so you price too low. If that cost isn’t recovered, your gross margin is a work of fiction.
✅ Preliminaries against programme. Welfare, scaffold, plant hire, supervision, site set-up. Priced once at tender against a programme, then spent every single week the job runs. When delays hit, these costs quietly eat your margin — track them weekly.
✅ Secured workload and pipeline. There’s no monthly recurring revenue in construction. Track the jobs you’ve won, the tenders awaiting a decision, and how often you actually win what you bid for. Then look ahead month by month. You might be busy today, but will you have enough work in six or seven months? Spotting the gap early gives you time to win work and plan staffing and cash.
✅ A rolling thirteen-week cash forecast. Not a budget. A week-by-week view of what’s coming in, what’s going out, and where it gets tight — updated every week, tied to certification dates rather than hope.
Why construction accounting needs specialist experience
Bookkeeping systems handle buying and selling. They struggle with construction.
Construction projects span months or even years, which means invoices raised and interim applications are recognised on percentage of completion, not on when a product is delivered.
You need a system that handles work in progress valued properly, accrued and deferred income treated consistently, and retention accounted for rather than forgotten. That means tracking applications, payments, retention and CIS status by subcontractor — and job costing that runs all the way down to contract level, not just a profit and loss for the company as a whole.
Then there’s the compliance
Heavier here than almost anywhere.
⚠️ CIS (Construction Industry Scheme). Verification before you pay any subbie, deduction at 20%, 30% or nil depending on status, monthly returns, and deductions suffered. Every subcontractor payment must be correctly categorised, verified and reported. Get the reclaim mechanism wrong and you’re lending HMRC money you badly need. This really bites when you go from a handful of jobs to several contracts running concurrently — the cost of guessing wrong escalates fast.
⚠️ The domestic VAT reverse charge. It changed the cash flow of every subcontractor it touched, and it remains one of the most commonly misapplied rules in the sector.
⚠️ VAT liability on the work itself. Zero-rated new dwellings, 5% on conversions and certain renovations, standard rate on most everything else. Charge 20% where you needn’t and you’ve made yourself uncompetitive. Charge zero or 5% where it should have been 20% and you’ll fund the difference out of your own margin when HMRC catches up, plus penalties and interest.
When you’re deducting CIS at source, managing reverse charge VAT on building services, and tracking project costs across multiple sites, your financial administration becomes genuinely specialised. Get the returns wrong and you face penalties. Misclassify workers and you face liability issues. Fail to claim capital allowances on commercial property improvements and you miss significant tax savings.
Continuous improvement belongs in the finance function too
If month-end takes three weeks, that’s a fifteen-day delay between something going wrong on site and anyone in the office finding out. On a twenty-week contract, that’s most of a phase.
If your WIP figure is a best guess until the year end, you’ve got no reliable margin data for eleven months of the year. And if the QS is working from one set of numbers and finance from another, nobody really knows your numbers.
Close faster, value WIP consistently, challenge the cost to complete on every live contract every month, and put real numbers in front of the people who can act on them. Then do it a bit better next month. Small gains, compounding — exactly the way it works on a job.
The bit almost everyone underestimates
Cross-functional working is the single biggest lever, and it costs nothing.
When commercial, site, buying and finance all work from the same numbers, the arguments stop and the decisions get better. The estimator stops pricing from old labour rates. Buying sees what a call-off is really doing to working capital. The contracts manager finds out early in the month that a job has slipped, not at final account eight months later — while there’s still time to do something about it.
This is where the right system earns its keep: job costing that talks to your accounts, your applications and your subcontract ledger, so commercial and finance data stay aligned instead of drifting into two versions of the truth. For some businesses that’s a well-run set of integrated packages. For others it’s construction-specific software. What matters is that there’s one set of numbers, not two.
And Don’t Leave the Tax Reliefs on the Table
Construction is better served by the UK tax system than most contractors realise, and worse at claiming than almost any sector.
R&D tax relief
This doesn’t require a laboratory. Solving a genuine technical problem where the answer wasn’t obvious — difficult ground conditions, an unusual structural solution, new materials, offsite and modern methods, hitting an energy performance standard nobody on the job had hit before — much of that can qualify. It’s routinely missed because the people doing the work see it as part of the job rather than anything special. The rules and evidence requirements have tightened considerably, so this is one to get properly assessed rather than assumed either way.
Capital allowances
These materially change the real cost of plant, machinery and vehicles, and the rules moved in 2026:
✔️ The Annual Investment Allowance still gives 100% relief on up to £1 million of qualifying plant and machinery a year, for companies and unincorporated businesses alike.
✔️ Full expensing gives limited companies uncapped 100% first-year relief on qualifying new main rate plant and machinery. Assets must be new and unused, and sole traders and partnerships are excluded.
✔️ A new 40% first-year allowance arrived on 1 January 2026 for qualifying main rate expenditure — aimed at spend that couldn’t reach full expensing or the AIA, notably assets for leasing and unincorporated businesses.
⚠️ The main pool writing down allowance fell from 18% to 14% from 1 April 2026 for companies. That only affects expenditure dropping into the main pool, but when it does, relief now arrives noticeably more slowly.
There’s also the structures and buildings allowance, and — frequently overlooked — the embedded fixtures in a commercial property you’ve bought, which are often worth a great deal and almost never claimed without someone going looking.
Land Remediation Relief
An enhanced deduction on qualifying costs of dealing with contaminated or long-derelict land. If you’re a developer taking on difficult sites, this is real money and it’s widely missed.
CIS gross payment status
Not a relief, but it does the same job. If you qualify, getting paid gross instead of net of 20% transforms your working capital position — and keeping your compliance record clean enough to hold onto it is worth building into how you run the business.
Where to start
You don’t need to fix everything at once. Pick the number that’s currently costing you the most — for most contractors it’s real-time margin by contract, or the cash locked up in retention and unbilled work — and get that one right first.
💡 Because the real question isn’t whether your numbers are perfect. It’s whether they’re good enough, and timely enough, to make the next decision well.
If they’re not, that’s worth a conversation. Book a free 30-minute call and let’s look at what your numbers are actually telling you.
#Construction #Contracting #CIS #CashFlow #WorkingCapital #Retention #VFD #CFO
