Cashflow is the single biggest reason UK construction businesses fail. Profitable businesses. Growing businesses. Businesses with strong order books. All can and do collapse when cashflow goes wrong, and it goes wrong more often in construction than in almost any other sector.
This guide covers why construction cashflow forecasting is different from other industries, how to build a forecast that actually reflects how construction firms get paid, and the specific factors (retentions, stage payments, CIS deductions, reverse charge VAT) that catch UK construction businesses out.
Why construction cashflow is different
Almost every other industry follows a broadly predictable pattern: you deliver something, you invoice for it, the customer pays within 30-60 days. Construction breaks every part of that model.
Stage payments
Construction work is rarely paid on completion. Most contracts are structured around applications for payment or stage payments, where you’re paid for work completed during a defined period (often monthly). This introduces a lag between doing the work, applying for payment, having the application certified, and receiving payment.
Retentions
Most construction contracts include a retention (typically 3-5% of contract value) that the customer holds back for the defects liability period, usually 6-12 months after practical completion. Half of the retention is often released on completion, the other half at end of defects period.
For a business with several active contracts, retention balances can grow into tens or hundreds of thousands of pounds — money that’s been earned but hasn’t landed in the bank.
CIS deductions
Subcontractors have 20% (or 30%) deducted from every invoice by their main contractor. That money is offset against the annual tax bill or refunded through Self Assessment/Corporation Tax, but it’s out of the business’s hands during the year.
Reverse charge VAT
Since March 2021, most construction subcontractors don’t collect VAT from their main contractor customers. Before reverse charge, a subcontractor invoicing £10,000 would receive £12,000 and hold the £2,000 VAT until the next quarterly return. That informal float has largely disappeared under reverse charge, meaning working capital is lower for the same trading level.
Long payment cycles from tier-one contractors
Some large main contractors and developers have payment terms of 60, 90, or even 120 days from application, despite the Prompt Payment Code and Small Business Commissioner. For subcontractors, this creates funding gaps between doing the work and receiving payment.
How to build a construction cashflow forecast
The industry-standard tool is a 13-week rolling cashflow forecast. Long enough to see problems coming. Short enough to be accurate. Updated weekly.
Step 1: List every source of cash coming in
- Applications for payment already submitted (with expected receipt dates based on customer payment terms)
- Applications for payment you expect to submit in the next 13 weeks
- Retentions releasing during the period (with realistic dates — they’re often late)
- CIS refunds due
- VAT refunds due (if repayment position)
- Any other income (asset sales, insurance claims, grant funding)
Step 2: List every cash outflow
- Wages and salaries (with payment dates)
- Subcontractor payments (net of CIS deductions you’ll withhold)
- Materials and plant hire
- Fuel and vehicle costs
- Rent, utilities, insurance
- VAT payments
- PAYE and CIS payments to HMRC (usually 22nd of month following)
- Corporation Tax payments
- Loan repayments and finance costs
Step 3: Time each item to the week it will actually hit the bank
This is where most forecasts fail. It’s not enough to know an invoice is due; you need to know when the customer will actually pay based on their history. A customer with 30-day payment terms but a track record of paying in 45 days should be forecast at 45 days, not 30.
Step 4: Track opening bank balance week by week
Add each week’s inflows, subtract each week’s outflows, and see where you end up. A forecast that shows the balance dipping negative in Week 6 is a forecast telling you to act now.
Step 5: Update weekly
A cashflow forecast that isn’t updated is a cashflow forecast that lies to you. Every Monday morning, refresh the actuals from the previous week and roll the forecast forward one week. Takes 30 minutes. Prevents disasters.
Construction-specific factors to build into your forecast
Retention tracking
Keep a separate schedule of every retention held against you, with expected release dates (both first half at practical completion and final half at end of defects liability). Cross-check against your forecast so you’re not double-counting or forgetting funds due.
CIS deductions on subcontractor payments
If you’re a main contractor, you’re deducting CIS from your subcontractors. That money isn’t yours — it needs to be paid to HMRC by the 22nd of the following month. Build this into your forecast as a separate line so it’s clearly earmarked.
VAT under reverse charge
If most of your work is under reverse charge, your quarterly VAT return will often show a repayment position (input tax on your purchases without matching output tax). Build these VAT refunds into your forecast, but be realistic about timing — HMRC repayments can take 30 days or more from the return date.
Materials and cash payment mismatches
Materials suppliers often want payment within 30 days. Main contractor customers often pay you 60+ days after your application. This creates a systematic cashflow gap that grows as your business grows. Trade credit terms with your key suppliers can significantly ease this.
Late payment reality
Construction has one of the worst late-payment records of any sector. Don’t build your forecast on optimistic assumptions. Build it on what your customers actually pay you, based on history. If they average 55 days, use 55, not 30.
Red flags to watch for
Debtor days creeping up
Track your average debtor days month-over-month. If they’re trending up, your customers are paying more slowly than they used to. This can be a sign of trouble on your customer’s side or a symptom of your own credit control weakening.
Retention balance growing faster than turnover
If total retentions held against you are growing as a percentage of turnover, more of your earned income is being locked up. Worth understanding why and when it will unwind.
Overdraft usage creeping up
If you’re using more of your overdraft facility for longer periods, that’s a warning that structural cashflow is tightening. Overdrafts are for smoothing genuinely short-term gaps, not for funding operations.
VAT and PAYE payments becoming difficult
If you’re struggling to pay HMRC on time, that’s a very clear signal. HMRC is patient but not indefinitely patient, and getting into arrears with HMRC restricts your options significantly.
Tools that help
Cloud accounting with cashflow integration
Xero, QuickBooks, and Sage all offer basic cashflow forecasting integrated with your live accounting data. Sufficient for many small construction businesses.
Specialist cashflow tools
Float, Fluidly, Fathom, and Futrli integrate with cloud accounting software and produce more sophisticated cashflow models. Worth the subscription for businesses turning over £1m+.
A well-built spreadsheet
For smaller businesses, a properly structured Excel or Google Sheets model can genuinely be enough. The discipline of updating it weekly matters more than the sophistication of the tool. A good accountant can build you a template in an afternoon.
When to escalate
If your forecast shows a genuine cash gap in the next 8-13 weeks:
- Talk to your accountant first. Sometimes there are options you haven’t considered (VAT payment plans, corporation tax deferrals, timing of costs)
- Talk to your bank. Extending overdraft facilities is much easier BEFORE you need the money, not after
- Look at invoice finance for construction-specific facilities that advance against applications for payment
- Chase outstanding debts hard — the Small Business Commissioner and Prompt Payment Code exist for a reason
- Talk to HMRC if tax payments are the issue — Time to Pay arrangements exist for businesses that engage early
The businesses that survive cashflow crises are almost always the ones that saw them coming 6-8 weeks out and acted. The ones that don’t survive are the ones that discovered the crisis on payday and had no time to react.
Frequently asked questions
How often should I update my construction cashflow forecast?
Weekly at minimum. Construction cashflow moves too quickly for monthly updates to catch problems in time. Every Monday, reconcile last week’s actuals against the forecast, roll the model forward one week, and review the next 13 weeks.
Should retentions be included in cashflow forecasts?
Yes, but only in the weeks they’re realistically expected to be released. A retention held for a defects liability period ending in 8 months should not appear in your 13-week forecast. A retention becoming due next month should. Keep a separate retention schedule so nothing gets missed.
How do reverse charge VAT rules affect my cashflow forecast?
If you’re a subcontractor invoicing under reverse charge, you won’t receive VAT from your customer, so your cash inflows are your net invoice amounts. You’ll likely be in a VAT repayment position each quarter (you’re reclaiming VAT on your purchases without matching output VAT), so build expected VAT refunds into your forecast on realistic dates.
Is invoice finance a good option for construction cashflow?
It can be, but construction-specific facilities are important. General invoice finance often excludes construction because of the application-for-payment structure, retentions, and dispute risk. Specialist providers understand these dynamics and can advance against applications rather than just invoices. Not cheap, but often the difference between winning and losing on tenders that would otherwise stretch your cashflow.
What’s a healthy cashflow buffer for a construction business?
A common benchmark is 3 months of overhead costs held in accessible cash. For construction, we’d argue for 4-6 months given the sector’s payment volatility. Businesses running with less than 6 weeks of buffer are effectively one late payment away from real trouble.
Cashflow is where construction businesses live or die. If yours is tighter than you’d like, or you’re winning work but nervous about funding it, send us a message. We help Kent construction firms build proper cashflow forecasts and put the right facilities in place before the pressure hits.
