If you've been fitting for years, you already know the obvious levers: buy well, don't waste time, don't undersell. This isn't about that. It's about the margin leaks that survive precisely because they don't look like problems, the ones that hide inside jobs you'd swear made money.
The market isn't doing you any favours either. Doors and windows were the fastest-rising construction product category in the UK, up 17.5% year on year at one point, and prices are still expected to climb roughly 4 to 6% a year (CPA / ONS data). In a sector where a healthy net margin is around 10% of turnover (Window News), that kind of input inflation eats a year's profit if your pricing doesn't move with it. So the bar isn't "work harder." It's "stop the quiet leaks before the market widens them."
Know the one number that actually decides this
Most fitters track turnover and what's in the bank. Neither tells you if you're winning. The number that does is gross margin percentage, and there's a well-established benchmark to measure yourself against: gross margin should sit at 30% or more of turnover, overheads at 20% or less, leaving a net profit of at least 10%. Once gross margin drops below 25%, it's highly improbable the business is actually making money (Window News).
Here's the trap that catches even experienced operators: margin and mark-up are not the same thing, and confusing them silently underprices everything you do. Take a job that costs you £1,000. Add a 30% mark-up and you sell at £1,300, which feels like a 30% margin. It isn't. Your gross profit is £300 on a £1,300 sale, a margin of just 23%, below the danger line. To actually make a 30% margin on that job you need to sell it at around £1,430, a mark-up of roughly 43%. If you've been "adding 30%" for years, you've been working to a 23% margin and wondering where the money went.
Treat your deposits as a warning light, not income
This is the most expensive blind spot in the trade right now. Across the industry, installers are fitting work that was sold four to six months ago at old prices, and in some cases completing jobs at a loss without realising it. Large customer deposits provide temporary liquidity, which masks the real position, because that cash is quietly covering the costs of previous jobs (Insight Data, from analysis of 15,000+ fenestration businesses).
A full bank account can mean you're profitable, or it can mean you're funding old work with new deposits. The two look identical until the order book thins. The discipline that protects you is per-job costing: knowing the true margin on each job as you complete it, not the blended feeling at month end. If you only learn the truth when cashflow tightens, you've learned it too late to reprice.
Reprice on a clock, not on a hunch
Because input costs are still rising at 4 to 6% annually, a price list is a depreciating asset. Quote off last year's costs and you give your margin away one job at a time. The fitters holding their margins aren't charging more out of bravado; they're simply re-checking their costs on a schedule and moving with the market.
Set a fixed cadence, quarterly at least, to rebuild a sample quote from current supplier pricing and current labour cost, then compare it to what you're actually charging for that work. Calculating job costs from real numbers is what turns "I think we're alright" into a figure you can defend. It also surfaces the job types that have quietly slipped underwater since you last looked.
Price the risk, not just the windows
Two jobs with identical units are not identical jobs. One has off-street parking and a decisive customer. The other has scaffold, a conservation officer, and a homeowner who's already changed the colour twice. They cost the same in materials and wildly different in callbacks, delays and aggravation, yet most quotes price only the visible work.
Margin is destroyed by the tail: the one job in ten that goes sideways. If you price for the average case and absorb the bad ones, your good jobs are quietly subsidising your worst. Build a deliberate premium into quotes for access problems, heritage work, or warning-sign customers. You'll either get paid for the difficulty or lose a job you'd have lost money on anyway. This is the same thinking behind why fitting firms lose money on jobs: the loss is rarely in the fitting, it's in the unpriced exceptions.
Make remakes the thing you measure
The single most expensive line in window fitting isn't on any price list. It's the remake. A measurement a few millimetres out means a new unit, a wasted delivery slot, a second visit and an awkward customer call. You've now paid for that opening twice and earned nothing extra, and at a 30% margin you need to sell roughly three more jobs just to recover one remake.
Experienced fitters don't avoid this with more skill; they avoid it with one survey standard everyone follows. The same fields captured the same way every time: opening sizes, cill type, glass spec, trickle vents, access. If you can't say what your remake rate was last quarter, that's the first thing worth measuring, because it's almost certainly costing more than your supplier prices. Keeping the schedule clean matters here too: a double-booked crew burns a whole visit that lands straight on your margin.
Make the leaks visible while you can still act
Every leak above shares one cause: you find out too late. The quote that undercharged, the job that ran two days over, the remake nobody logged, the deposit covering an old loss. When quotes, orders, schedule and costs live in separate apps and notebooks, the picture only assembles itself at month end, long after the money's gone.
The fix is putting the whole job on one record so margin is something you watch, not something you reconstruct. FitterPal pulls quoting, ordering, scheduling and job costs together so you can see quoted-versus-actual per job, spot the work that ran over, and catch a slipping margin while there's still time to do something about it.
Where to start
Don't try to fix all of this at once. Start with the number: work out your real gross margin percentage on the last ten jobs, using true costs, not the quote. If it's under 30%, you have your answer and your priority. If your deposits are healthy but you can't say which jobs actually profited, fix costing visibility before you chase more work, because more work at a hidden loss just gets you there faster.
None of this is about working harder. The fitters who keep their margins in a tightening market aren't grafting more hours; they know their numbers, they price the risk, and they see the leaks early enough to plug them.
