How to compare three builders' quotes that do not match
Three quotes for the same extension arrive at £38,000, £47,500 and £52,000, and the natural reading is cheap, middle, dear. That reading is usually wrong. Most of the spread between quotes is differences in what is included, not differences in price for the same work, so the job is to make the quotes describe the same project before letting the totals argue. Do that and the cheap quote is quite often the dear one.
Normalise the scope first
Go through each quote and answer the same questions of it. Where does the work start and stop: is making good included, is decoration, is rubbish removal, is the scaffold? Which materials are supplied by the builder and which are yours to buy? Are the drains, the electrics and the plastering in the price or named as someone else's problem? A one-page grid with a row per work item and a column per builder turns an unreadable comparison into a visible one, and the empty cells are the finding.
Find the provisional sums, because that is where the price moves
A provisional sum or PC sum is an allowance for something not yet priced: "allow £3,000 for kitchen fitting", "PC sum £40 per square metre for tiles". They are legitimate and unavoidable, and they are also where a low quote hides. A quote that is £6,000 cheaper and carries £8,000 of provisional sums is not cheaper, it is less finished, and every provisional sum is a price that will be set later, when your negotiating position is a hole in the wall.
Then normalise the money
Check the VAT position explicitly: a VAT-registered builder's £40,000 plus VAT is £48,000 against a smaller firm's £45,000 inclusive, and quotes are routinely silent about which they are. Check what happens to the price over time: is it fixed for the duration, or open to material price rises? And check the payment schedule, because money is part of price: staged payments against completed work are normal, while a large deposit against work not yet started is your risk transferred to you, priced at zero.
Read the silences
The most informative parts of a quote are the things it does not say. No breakdown, only a total, means no way to compare and no basis for pricing changes later. Nothing about how variations will be priced means arguments later, at hole-in-the-wall rates. No start date or duration means your project is the flexible one in his schedule. A very round number arrived at very quickly tells you how much attention your job got. None of these is disqualifying alone; each is a question to ask before signing rather than after.
Cheapest, dearest, and what to actually pick
The spread itself is information about risk. If one quote is far below the others, the likeliest explanations are a scope gap, a misread job, or a firm that needs the work badly, and all three become your problem after the deposit clears. Aim for three genuinely comparable quotes; two is a coin toss and one is not a market. Then pick on the whole picture: normalised price, the specificity of the document, how the firm handled questions, and references from jobs like yours, weighted roughly in that order.
Common questions
The cheapest quote is £10,000 under the others. Is that a red flag?
Treat it as one until proven otherwise. Reconcile it line by line against the fullest quote and the gap almost always resolves into missing scope or provisional sums rather than efficiency. If it genuinely is the same job for less, the paperwork will survive the comparison, and that is the test.
Should I tell builders what the others quoted?
Sharing the number invites pricing to the number. It is more useful to share scope: give every builder the same written description, ask each to quote against it item by item, and the comparison largely builds itself.
How many quotes are enough?
Three comparable ones for anything substantial. Beyond four or five the returns fall fast, good firms start declining to bid, and the delay starts costing more than the comparison saves.