Is my builder's quote reasonable?
Three quotes for the same kitchen. £14,000. £19,500. £23,000. None of them is obviously wrong. None of them is obviously right either. The job is to figure out which one is reasonable, and what "reasonable" actually means when the spread is over 60%.
This guide gives you three concrete methods to do that, the five red flags that should stop the conversation regardless of price, and a working definition of "reasonable" that holds up when you're staring at a builder's number trying to decide.
You don't need an independent surveyor for most domestic work. You need a baseline, a line-item check, and a sense of what other homeowners with similar properties have actually paid.
The 30% spread: why like-for-like quotes vary so much
When two quotes are for genuinely the same scope with the same assumptions, the typical spread is 5–10% (HomeOwners Alliance, Federation of Master Builders). When the scope is loosely defined or assumptions differ, you'll see 30% or more. The wider spread is what most homeowners actually encounter, because most quotes aren't truly like-for-like.
Two builders looking at the same job make different assumptions about what's behind the walls, what level of "making good" they're including, how much waste they're carrying, and how busy they are this quarter. None of that is dishonest. It's how pricing variation works when scope leaves room for interpretation.
The spread itself isn't a red flag. It's a diagnostic. A 30% spread tells you the quotes aren't comparing the same thing yet. Your job is to bring all three quotes to the same scope before you compare numbers.
We hit this directly when we got three quotes to plaster a single room. The cheapest was for a simple skim. The middle quote added extensive repair to the inside of an external wall. The most expensive added all that plus replacing a bowing ceiling. We picked the middle quote because it felt like the sensible choice. Two weeks into the work, it became obvious the ceiling needed replacing anyway. The total cost ended up matching the most expensive quote. But the sequencing was now wrong: the ceiling work that should have happened first happened last, and everything around it had to be redone.
Three methods to validate a quote
Each of these takes 15–30 minutes. Done together, they'll get you to a reasonable confidence level on a domestic renovation quote without paying for an independent surveyor.
Method 1 — Calculator triangulation
Before you accept any quote, set a baseline number for what the project should cost in your postcode. Most renovation calculators give you a regional-adjusted range based on size, finish level and project type. The gap between your baseline and the quote tells you whether the quote is broadly aligned or wildly out.
For a kitchen, see what a kitchen renovation should actually cost in your area→. For a bathroom, see what a bathroom renovation should actually cost in your area→. For plastering, see what plastering should cost for your room→.
If the quote sits inside the regional range, the headline number is reasonable. If it's 25% or more above or below, dig into why. Above usually means premium specifications. Below usually means scope omissions.
Method 2 — Materials line-item check
If the quote breaks materials out separately (it should be itemised; every reasonable quote breaks materials out from labour), you can verify each line. Materials calculators give you an independent benchmark for what the materials line should cost based on the work specified.
For paint, calculate exactly how much paint you'll need for the room→. For tile, calculate exactly how many tiles you'll need including wastage allowance→. For flooring, calculate exact flooring quantities for your room shape→.
If the materials line is 20% or more above the calculator benchmark, ask the builder to break out brand and supplier. They may be specifying premium products you didn't ask for. If it's well below, ask what wastage allowance they've used, because under-ordering is what causes the half-day delay halfway through the project.
Method 3 — Community check
Mumsnet's Property and DIY boards and r/DIYUK on Reddit are full of homeowners who've recently done similar projects in similar properties. Post your scope and your quote, redact identifying details about your address and your builder, and ask specifically about line items that look high or low.
The signal-to-noise ratio is better than most people expect, because the people answering have just been through it themselves. Aim for replies from homeowners with the same property era (Victorian terrace, 1930s semi, post-war estate) and the same region. What a kitchen costs in Manchester is different to what it costs in Brighton.
Five red flags that should stop the conversation
Some things in a quote aren't pricing problems. They're risk problems. The five flags below should stop the conversation regardless of price.
No written quote. A verbal quote isn't a quote. No scope, no exclusions, no payment terms, no consumer protection. Walk away.
Large upfront payment. A reasonable deposit is 10–20% on contract signing or first day on site. Anything above 30% upfront means you're paying for work that hasn't started, with no security if the builder walks. Stage payments after the deposit should tie to completed milestones (first fix complete, second fix complete, snagging signed off), not calendar dates.
No VAT registration when expected. If a builder is operating above £85,000 annual turnover, they should be VAT-registered (current GOV.UK threshold). If their turnover justifies you spending £20,000+ with them but they aren't VAT-registered, the maths doesn't work. Verify on GOV.UK before signing.
Cash-only insistence. Cash leaves no audit trail, often signals VAT avoidance, and forfeits consumer protection. A reputable builder takes bank transfer and issues a VAT invoice if they're registered.
Vague exclusions."Subject to site conditions," "all reasonable preparation," "normal making good" give the builder the right to charge extra for almost anything later. Push back. Get specifics in writing.
Why the cheapest quote is rarely the best
Three quotes come in. Cheapest wins, except it doesn't, because the cheapest is usually the one with the most omitted.
Common omissions in budget quotes: decoration ("paint not included"), "making good" plasterwork after first fix, waste removal, snagging beyond the headline date, longer warranty period. None of those vanish. They get added back later as "extras" or done badly because the budget didn't allow proper time.
To compare quotes properly, force them to the same scope. Take the most detailed quote (usually the most expensive). For each line item, ask the cheaper quotes whether that line is included, excluded, or assumed. Once scope is equalised, the price spread usually compresses to the FMB / HOA 5–10% range, and the original price advantage often disappears.
What "reasonable" actually means
Three things, all required:
The headline number sits within the FMB / HOA range for your project type, region and finish level. If you've done Method 1 and the quote falls inside the regional band, that condition is met.
The scope is complete and written down. Every line itemised. Exclusions explicit. Variation procedure stated. If you can't tell what you're getting for the money, the price is meaningless.
The trader is verifiable. VAT-registered if appropriate, registered with the relevant trade body (NICEIC for electrical, Gas Safe for gas, FENSA for windows), confirmed on Companies House, with references you can actually call.
A cheaper quote that fails on scope completeness isn't reasonable. An expensive one that passes all three tests is reasonable, even if you'd rather pay less.
For broader cost context across all renovation types, see our complete guide to UK renovation costs→.
Frequently asked questions
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