Construction in London is hard enough without your accounts looking like the Big One at Blackpool. One month the job books show a fat 50 % net profit; the next month it crashes to 3 %. Spoiler: the projects didn’t suddenly go bad—your reporting did.
Below we unpack why this happens, how accrual management accounts fix it, and the simple tweaks you can make this week to see reliable trends that sharpen pricing, protect cash flow and keep HMRC happy.
See how we help construction businesses here.
Why Construction Margins Yo‑Yo
| Common Issue | How It Skews Results |
|---|---|
| Applications vs Invoices | Raise an application on 28 July, but the invoice on 5 August and July’s revenue vanishes from the P&L. |
| Up‑front Material Purchases | Buy the steel in Month 1, recognise revenue in Month 3 – Month 1 looks loss‑making. |
| Retention Adjustments | Holdbacks often sit in debtors instead of being split into current vs long‑term, overstating short‑term profit. |
| Labour Allocation | Weekly payroll coded to “Overheads” instead of each site. Over/under‑costing every project. |
The Accrual Accounting Fix (Match Costs to Revenue)
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Cut‑off Discipline
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Post labour, plant and materials to the month they’re used, not the month they’re paid.
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Use supplier accrual journals where invoices arrive late.
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Revenue Recognition per Valuation
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Record revenue when the application is certified, even if the invoice lands next month.
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In Xero, raise a manual journal dated to the valuation period and reverse it the day the invoice is issued.
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Monthly Management Accounts
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Close‑off ledgers by the 10th working day.
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Review WIP, retentions, CIS, and site‑level gross profit every month—not once a year.
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Job Costing Discipline
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Tag every transaction to a tracking category (site, phase or cost code).
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Reconcile timesheets to payroll before posting.
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Consistent Margin Review
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Track rolling 3‑, 6‑ and 12‑month averages.
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Flag any swing >5 pts for a quick root‑cause check.
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Quick Win: Correcting July/August Application Timing
Scenario: Application raised 28 July, invoice raised 5 August. July’s income disappears.
Fix
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Create a journal dated 31 July:
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Dr Applications Receivable £ X
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Cr Revenue £ X
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On 5 August, post the invoice to clear Applications Receivable.
Result: July now shows the real project profit, and August starts clean.
Case Snapshot – London Fit‑Out Contractor
| Before | After Six Months with Proper Accruals |
|---|---|
| Net profit swing 45 pts in 60 days | Net profit variance <7 pts quarter‑on‑quarter |
| Bank asking for extra security | £250k RCF approved on the back of robust MI |
| Directors priced jobs on gut feel | Pricing model updated monthly with live gross margin data |
FAQ for London Builders
Does this change my tax bill?
No. Corporation Tax is still calculated on the year‑end accounts, but better in‑year visibility lets you plan payments and avoid nasty surprises.
We already use Xero—do we need new software?
Probably not. Xero + Projects (or a bolt‑on like WorkflowMax) handles accrual journals, cost coding and reporting. The gap is usually process and discipline.
Our bookkeeper is part‑time. Who owns the month‑end?
Make one person (internal or outsourced) accountable for: (1) cut‑off, (2) WIP schedules, and (3) the management pack. Many London firms use a Virtual Finance Office (VFO) for exactly this.
Next Steps for Steadier Margins
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Audit last quarter’s P&L for timing errors—start with applications and labour.
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Build a Month‑End Checklist (downloadable template coming soon).
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Book a 30‑minute Discovery Call here with us to see how many margin points are hiding in your data.
