Why cash flow, not profit, decides which window firms survive

Profit is an opinion. Cash is a fact. You can have a diary full of work, a healthy margin on every job, and an accountant telling you the year looks strong, and still find yourself unable to pay your supplier on the 30th. That gap between "profitable" and "solvent" is where most window installation businesses get into trouble, and it is almost never because the work was bad.

The numbers bear it out. Construction recorded 3,803 company insolvencies in the 12 months to May 2026, the highest of any sector in the economy (Insolvency Service). The firms that go under are rarely the ones doing poor work. They are the ones who ran out of cash before the cash ran in. So the question worth obsessing over isn't "are my jobs profitable?" It's "when does the money actually arrive, and what do I owe before it does?"

The gap that catches everyone: you pay before you get paid

Walk a single job through on a timeline and the problem is obvious. You order materials and pay for them, or you're invoiced on 30-day terms. You pay your installers weekly. You run the van, the insurance, the FENSAUnderstanding CIS: A Guide for InstallersRegister correctly, verify subcontractors, apply the right CIS rate, and keep clean monthly records so you avoid 30% deductions and HMRC penalties. admin. All of that goes out before the customer pays the balance on completion. On a £6,000 retrofit, you might be £3,500 out of pocket for two or three weeks before a penny comes back.

Now multiply that across every live job. The more work you win, the bigger the gap, which is the cruel twist: growth eats cash. A busy month can leave you with less in the bank than a quiet one, because you've funded more materials and more labour upfront. And the gap is widening on its own. Plastic doors and windows rose 5.6% in the 12 months to February 2026 (DBT building materials statistics), so the amount you have to lay out before getting paid keeps creeping up, even when your prices and margins hold.

Understanding this gap is the whole game. Everything below is about shrinking it.

Deposits and staged payments are your cheapest finance

The single biggest lever a domestic installer has is the payment structure, and most leave it loose. A deposit isn't a nice-to-have or a sign of distrust. It is the cheapest working capital you will ever access: interest-free, paid by the person who wants the work done.

Structure it so the customer's money funds the job, not yours:

• Deposit on order, sized to cover materials. Not a token 10%. Enough to pay for the glass and frames so you're never buying stock against your own overdraft.
• A stage payment at the start of the install on larger jobs, so labour is covered as it's incurred.
• Balance due on completion, invoiced the same day, not "end of the month".

The discipline that makes this work is simple and non-negotiable: never order materials before the deposit has cleared. Ordering on a verbal yes is how installers end up bankrolling customers who then go quiet. This is the same failure mode behind a lot of the avoidable losses covered in why window fitting companies lose money on jobsWhy Window Fitting Companies Lose Money On JobsJobs rarely lose money in dramatic ways, they bleed it in measurable places you can't see unless you compare what you quoted with what the job actually cost, which is the one habit most fitters skip., and it's one of the fastest ways to improve your marginsImprove Your Margins: Practical Tips for a More Profitable Window Fitting BusinessImprove your window fitting margins by buying smarter, scheduling tighter, standardising how jobs are run, and pricing from real costs instead of guesswork. without raising a single price.

Let customers spread the cost and get paid in full upfront

Offering finance at the point of sale is one of the most underused cash-flow tools in the trade, and it's widely misunderstood. The benefit isn't that the customer "pays on time". It's that the lender pays you the full job value upfront, minus a subsidy fee, and then the customer repays the lender over months or years. Your wait and your debtor risk don't shrink, they vanish. You're paid in days, on someone else's balance sheet.

There's a second prize. A £9,000 whole-house job is a daunting cheque, but £150 a month isn't, so finance lifts your conversion rate and your average order value at the same time. Customers who'd have done the front of the house say yes to the lot, or trade up to the better glass, because the decision becomes affordability per month rather than cash in the bank today.

Two caveats keep this clean. First, get the terminology and the rules right: classic buy now pay later suits small purchases, while big-ticket window work runs on regulated point-of-sale home improvement credit, and the FCA brings the remaining unregulated deferred payment credit into its perimeter on 15 July 2026 (FCA). If you introduce customers to a lender, particularly in their home, you'll generally need FCA credit broking permissions or you work through an authorised provider. Second, price the subsidy fee into the job. Finance is a sales and cash-flow tool, not free money, and the convenience should never quietly eat the margin you worked out in your job costsCalculating Job Costs: Tools and Tips for Accurate QuotesJobs that look fine on the quote still leak margin when you skip consumables, overhead and contingency, and tight costing with real labour and supplier numbers is how you stop donating profit..

Get the invoice out the day you finish

Here is a cost that is entirely self-inflicted: the lag between finishing a job and sending the invoice. Every day the invoice sits unsent is a day added to how long you wait for money you've already earned. If you finish on Tuesday and invoice "when I get to the paperwork at the weekend", you've voluntarily extended your own debtor days.

Late invoicing compounds with late paying. Even disciplined firms wait, and the wait is getting worse: 93% of construction and property firms reported late payments in 2026, running an average of 53 days overdue (Menzies, via Construction Industry News). You can't control how slowly a customer pays, but you can control the only two levers you actually own: how fast the invoice goes out, and how consistently you chase it. Treat chasing money with the same rigour you'd give to chasing a quoteWhy your window fitting quotes keep going cold (and the follow-up system that fixes it)Most quotes go cold from inertia, not price, and a timed follow-up sequence on every outstanding quote is the cheapest way to lift win rate without booking another survey., because an unpaid invoice is just a sale you haven't finished closing.

If you touch new-build or commercial, respect retention

Domestic work pays relatively quickly. Commercial and new-build work does not, and it carries a specific trap that has sunk plenty of capable specialist installers: retention. A main contractor typically holds back around 4.8% of your contract value as security, half released at practical completion and half a year or more later (government retentions review). That's money you've earned, sitting in someone else's account, exposed to their solvency, not yours.

And the exposure is real. The same review found 44% of contractors had retention money go unpaid because a firm above them in the chain went insolvent, at an average loss of £79,900. The lesson isn't to avoid commercial work. It's to price retention in, track every penny owed to you, and never let a single large slow-paying contract become big enough to take you down with it. Account properly for CIS deductionsUnderstanding CIS: A Guide for InstallersRegister correctly, verify subcontractors, apply the right CIS rate, and keep clean monthly records so you avoid 30% deductions and HMRC penalties. on this work too, because misreading what's withheld is another way the cash picture flatters to deceive.

Watch the runway, not just the balance

Your bank balance tells you about the past. Cash flow management is about the future: what's coming in, what's going out, and whether the two line up week by week. The firms that fail rarely see it coming, because they watch the balance instead of the runway. Across the sector, the average firm now expects to hit serious financial distress within eight months if conditions hold, and one in five are already financing their own projects while they wait to be paid.

You don't need accounting software to fix this. A rolling 13-week view (deposits due, invoices outstanding, supplier payments, wages, VAT) tells you where the squeeze lands before it arrives, so you can pull a job forward, chase a balance, or hold an order. Pair that with a cash buffer of a month or so of fixed costs, and a slow-paying customer becomes an annoyance rather than an emergency. Knowing your true job costsCalculating Job Costs: Tools and Tips for Accurate QuotesJobs that look fine on the quote still leak margin when you skip consumables, overhead and contingency, and tight costing with real labour and supplier numbers is how you stop donating profit. is what makes the forecast trustworthy rather than a guess.

Use credit as a bridge, not a crutch

Even with deposits, fast invoicing and customer finance, turbulent conditions still open gaps: a material price spike, a big contract that pays slow, a quiet quarter. The right job for external credit is to bridge a timing gap you can see coming, not to plug a structural hole. Used that way it's cheap insurance. Used to cover losses you haven't fixed, it's the first step of a spiral.

Match the facility to the gap. An overdraft or revolving line of credit covers short, lumpy shortfalls between paying suppliers and getting paid. Invoice finance releases cash tied up in unpaid invoices, which is exactly the money retention and 53-day terms lock away. Asset finance spreads the cost of a van or plant so a single purchase doesn't drain your buffer, and frees that capital to keep growing the businessSmart ways to invest in your window fitting companyTreat every pound you put back into the business as capital with an expected return, and the ranking is clear: retention, people and systems beat shiny kit, and they compound into a more valuable company. instead. For installers who can't get terms on their own, the government-backed Growth Guarantee Scheme gives lenders a 70% guarantee on facilities up to £2m for firms turning over under £45m, covering term loans, overdrafts, asset and invoice finance, and now runs to March 2030 (British Business Bank). Worth knowing: you remain 100% liable for the debt, so it widens access, it doesn't remove the risk.

The golden rule is to arrange credit before you need it. Lenders are wariest of firms already in trouble, and most schemes, the Growth Guarantee Scheme included, exclude a business in difficulty. A facility set up while you're healthy and left undrawn is a safety net. The same facility begged for in a panic is expensive and often unavailable.

Make the system do the chasing

All of this is just discipline, and discipline is hard to sustain by hand across thirty live jobs. This is where the right system earns its keep: tying deposits to the point a job is confirmed, prompting the invoice the moment work is signed off, and surfacing every balance that's overdue before it slips your mind.

FitterPal is built around exactly this. SmartStages ties payment steps to where each job actually is, so deposits get taken before materials are ordered and nothing reaches completion without an invoice going out. You stop carrying the cash position in your head and start seeing it clearly: who owes what, what's overdue, and where the next squeeze is coming from.

Profit will look after itself if the work is good and the pricing is right. Cash is the one you have to manage deliberately. Engineer the timing, and you remove the single most common reason good window firms disappear.

Book a demo and we'll show you how FitterPal keeps deposits, invoices and overdue balances in front of you, not lost in the admin.