The hard fact about this trade is how little of your turnover you keep. Specialty trades in UK construction run on net margins of around 2%, and even the country's 100 largest construction firms averaged just 1.7% in 2024 (The Access Group, citing Turner & Townsend and ONS). At 2% net, a single mispriced job or one half-day lost to a return trip can wipe out the profit on a week's work.
That changes how you should think about profitability. The best firms aren't meaningfully better at fitting windows than you are. They're better at protecting percentage points, and at a 2% margin, a few points reclaimed is the difference between a good year and a year you worked for nothing. Here's where those points actually live.
Price is the lever you're most afraid to pull
Of every way to improve profit, pricing is by far the most powerful and the most underused. Analysis of 1,200 of the world's largest companies found a 1% rise in price delivers an average 8.7% improvement in profit, dwarfing the 5.9% from cutting variable costs and the 1.8% from trimming fixed ones (McKinsey, The Price Advantage, via IndustryWeek). In a thin-margin trade, holding your price is the highest-leverage thing you can do all year.
Two traps stop fitters from getting this right. The first is mistaking mark-up for margin. Add 30% to a £1,000 job and you sell at £1,300, but your gross margin is £300 on £1,300, which is 23%, not 30%. To actually make a 30% margin you need a 43% mark-up (Window News). Plenty of firms quote on a mark-up they think is healthy and quietly run themselves into the ground. The second trap is competing on price. The market is already squeezing the top end: analysis of over 210,000 installer quotes found bifolds being fitted for under £1,000 per leaf in some areas, a historic low (Tommy Trinder, via GGP). Racing that to the bottom is a race to insolvency.
The way out is pricing from real numbers, not gut feel, so you know your floor and defend it. That starts with knowing your true job costs and understanding the margin maths cold.
Stop giving back the points you've already earned
Pricing wins points at the front of the job. Rework loses them at the back, and the leak is bigger than most owners realise. Across construction, the direct cost of avoidable error runs at about 5% of project value, set against that roughly 3% average margin (Get It Right Initiative). It's harsh, but the cost of getting it wrong can exceed the profit in the job entirely.
For a fitter, rework is rarely exotic. It's the wrong measurement that means re-ordering a unit, the return visit because the van went out without the right kit, the snag that should have been caught at survey. Every one of those is paid for twice, once to do and once to redo, and it comes straight off a 2% margin. Cutting rework isn't about working more carefully in some vague sense; it's about catching mistakes at the cheapest possible moment, which is before the van leaves.
Sweat your capacity, because your overheads don't care
Your rent, your van, your insurance and your core wages are fixed: they cost the same whether you fit four jobs this week or six. That's why scheduling is a profit lever, not just an admin task. Every billable day you squeeze from the same fixed-cost base falls almost entirely to the bottom line, and every idle half-day from a double-booking or a gap in the diary is pure loss.
The best firms run a tight, visible schedule so crews move from job to job without dead time, and so a cancellation gets backfilled instead of becoming a paid day off. On a thin margin, the firm that gets five productive days a week out of the same overheads as a rival getting four is simply more profitable, with no extra work won.
Market steadily so you never have to discount
Feast and famine is expensive at both ends. The quiet weeks burn fixed costs with no revenue against them, and the panic that follows pushes you into discounting just to fill the diary, which is the pricing mistake above made under pressure. A steady pipeline is what lets you hold your price, because you're never desperate for the next job.
That doesn't mean a big ad budget. It means consistent visibility and a reputation that keeps referrals coming, so leads arrive year-round rather than in bursts. The detail of building that sits in getting more customers, but the profit point is simple: consistent demand is what gives you the confidence to never sell cheap.
Invest in the crew that protects the margin
People are where pricing, rework and scheduling all meet. An experienced, well-trained fitter is the one who measures right first time, works clean and fast, and leaves a customer who refers the next job. That same fitter is your cheapest defence against the 5% rework figure and your best source of free, word-of-mouth leads.
Training and retention aren't soft costs, they're margin protection. A green crew making avoidable mistakes erodes the exact percentage points the rest of this article is about reclaiming, while a stable, capable one compounds quality and reputation over time.
Where to start
Profitability in this trade isn't won by fitting more windows. It's won by keeping more of what each window earns. Start with the two biggest levers: know your real numbers well enough to price with confidence and stop quoting on a mark-up that's secretly a loss, and attack rework so you're not paying for jobs twice.
Most of this depends on having your quoting, scheduling, job notes and follow-ups in one place rather than scattered across paper and phones, because that's what makes accurate pricing, tight diaries and caught-early mistakes possible day to day. FitterPal pulls it together so the small percentage points stop slipping through the cracks, and at a 2% margin, those points are the whole game. For the wider operating picture, see how to organise a window fitting business.
