How to compare builders' quotes line by line

By James Reilly, Swanbourne Construction Ltd · Published 15 October 2026 · Consumer law and VAT figures checked October 2026

To compare builders' quotes properly, put them on the same footing before you look at the totals. Check that each one is a fixed quotation rather than an estimate, list every exclusion and every provisional sum, make sure VAT is treated the same way in both, and line up the payment terms. Only then is the difference between the two numbers telling you anything about price rather than about what each builder left out.

We get handed other builders' quotations all the time — it is what our price match guarantee invites people to do. Most of the time the gap between two prices is not one builder being greedy and the other being generous. It is two different jobs written up under the same heading. This guide shows you how to find that out yourself, at the kitchen table, before you sign anything.

First: is it a quote or an estimate?

The two words get used as though they mean the same thing. They do not.

A quotation is a fixed price for a defined piece of work. If the work described is the work done, the price is the price. An estimate is the builder's best guess, and the final bill can move — sometimes a long way — without anybody having done anything wrong. What matters is not the word printed at the top of the page but what the document actually says: look for wording that makes the figure binding, and for wording that makes it "subject to" anything.

Once you accept a genuine quotation it is binding, even if the price of timber or steel goes up before the job starts. Citizens Advice is clear that a trader can only charge more where you asked for extra work, agreed to pay for extra work they told you was needed, or there was an obvious pricing mistake. An estimate can rise, but the final bill still has to be reasonable. And where no price is agreed at all, the Consumer Rights Act 2015 says you only have to pay a reasonable price. That is a safety net, not a plan. You want a number in writing before work starts — and a date it is valid until.

Make sure both quotes describe the same job

A one-page quote that says "build single-storey rear extension as per drawings, £58,000" and a forty-page quote that prices every line are not comparable until you have worked out what sits inside the first one. Go through the bigger document and tick off each item in the smaller one. Anything you cannot find is either included and unmentioned, or not included at all. Ask which.

The items that most often go missing from a short quote are the expensive ones:

• Foundations beyond a stated depth. One builder prices 1m-deep trench fill, another prices whatever the ground needs. On the coastal plain around Bognor Regis and Pagham, where high groundwater and soft clays are common, the difference can be thousands.
• Making good and decorating where the new work meets the old — the plastering, the skirting, the painting of the room you knocked through into.
• Scaffolding, especially on a loft, for the whole programme rather than a fortnight.
• Skips and waste removal, and how many.
• Electrics and heating in the new space, and whether the consumer unit or boiler needs upgrading to cope.
• Drainage, including moving a manhole or building over a public sewer.
• Glazing — the bifolds and roof lanterns are often the single biggest supplied item on an extension, and "allowance for" is not the same as "supply and fit".
• Kitchen, bathroom and flooring — supplied by the builder, by you, or not mentioned.

Provisional sums and prime cost sums

Every honest quotation has some of these, because some things cannot be priced until the ground is open or you have chosen a product. The question is how many there are and how realistic they look.

The trick to watch for is the deliberately low allowance. A quote that puts £1,000 against a bathroom suite when you have already picked one costing £3,500 looks £2,500 cheaper than one that priced the suite you want. Neither is wrong. Only one of them is telling you what you will actually pay. Rewrite every PC sum in both quotes to the same figure, and every provisional sum to a figure you believe, and then compare.

VAT: is it in or out?

This catches out more people than anything else, and it is a 20% swing. A builder who is not VAT-registered does not charge it. A builder who is registered must, and some show prices without it on the page.

The VAT registration threshold has been £90,000 of taxable turnover a year since April 2024. Most firms doing extensions and lofts at any volume are over it. If one quote is plus VAT and the other is not, add 20% to the first before you compare — as a homeowner you cannot reclaim it, so the VAT-inclusive figure is what leaves your account. You can check that a VAT number on a quote is genuine with HMRC's online VAT number checker.

Our prices are shown including VAT, on the price guide and on every quotation, with the VAT as its own line. Some work for disabled people can be zero-rated, which is a separate subject — ask if it applies to you.

Preliminaries: the costs of running the site

"Prelims" are what it costs to have a site at all: scaffolding, welfare facilities, temporary protection, skips, setting out, the builder's own management time, and insurance. On a big job they can be 10–15% of the price. Some quotes list them, some spread them across every line, and some leave them out and add them later.

If one quote shows a prelims section and the other does not, ask the second builder where those costs are. "We don't charge for that" usually means "it's somewhere else" or "you'll be paying for it later".

Payment terms tell you as much as the price

Two quotes at the same total can carry very different risk depending on when the money moves. Lay out each payment schedule side by side:

• The deposit. A modest deposit to cover materials ordered for your job is normal. Citizens Advice suggests not agreeing to a deposit of more than 25%, and getting a receipt. A large up-front payment before anything is on site — a third, a half — puts your money ahead of the work, and that is the situation that goes wrong.
• Stage payments versus valuations. Stage payments are tied to milestones ("roof on"). Valuations are tied to measured work done. Either can be fair; what matters is that you never pay for more than has been built.
• Retention. A small percentage held back until the job is genuinely finished gives you leverage over snagging.
• Payment method. Bank transfer to a business account, or card, against an invoice. Paying a deposit by credit card can bring Section 75 protection for amounts between £100.01 and £30,000. Cash only, or into a personal account, is a warning sign.

Ours is a 5% deposit, fortnightly valuations of work actually done, and 5% retention released at practical completion — set out on how we run a job. We are not saying that is the only fair arrangement. We are saying it is a good one to measure others against.

Variations: how is extra work priced?

Every job has changes. You decide you want an extra socket, a different window, a wall moved 300mm. The question is how the quote says those changes will be priced. Look for:

• A requirement that every variation is priced and agreed in writing before the work is done.
• Day rates for labour, so extra work has a known basis.
• What happens to the programme when something is added.

A quote with a very low headline and a vague variations clause is the classic way a £60,000 job becomes an £80,000 one. If the builder will not tell you their day rate before you sign, you will find out what it is afterwards.

The contract and the paperwork

A quotation is not a contract on its own, though it can form part of one. For anything beyond small works you want a written contract that covers the price, the scope, the programme, the payment terms, variations, insurance, and what happens if either side wants to end it. Off-the-shelf options exist — the JCT Home Owner contracts (the 2021 editions are current), the RIBA Domestic Building Contract, and the Federation of Master Builders' own contracts — or the builder may provide a contract written for the job. Whichever it is, read it before you sign.

Two pieces of law sit underneath every domestic building contract whatever the paperwork says:

• Under the Consumer Rights Act 2015, the work must be done with reasonable care and skill, and where no time is fixed, within a reasonable time. If it falls short you can ask for it to be put right at the builder's cost, and failing that a price reduction. A contract term that tries to exclude the care-and-skill duty does not bind you.
• If you sign the contract at home rather than at the builder's premises, you normally have a 14-day cancellation period under the Consumer Contracts Regulations 2013. If you want work to start inside those 14 days you have to ask for it in writing, and you may then have to pay a proportionate amount for work already done if you cancel. A builder who never gave you the cancellation information cannot charge for work done in that period.

The Construction (Design and Management) Regulations 2015 apply to domestic jobs too. On a domestic project the client duties pass automatically to the contractor, or to the principal contractor where there is more than one, so a good quote should mention how the builder will meet them. A builder who has never heard of CDM is telling you something.

A worked example: two extension quotes

Here is the sort of comparison we sit down and do with people. These are illustrative figures, not anyone's real quote, for the same 25m² single-storey rear extension in Bognor Regis.

On paper Quote A is £9,000 cheaper. Once the excluded electrics and heating, the making good, a realistic figure for the glazing and the skips are added back, the gap closes — and you would be handing over nearly £19,000 before a trench is dug. That is the comparison that matters.

Red flags in a builder's quote

• No company name, address or landline — or a mobile number only.
• No written scope: just a total and a signature line.
• "Plus extras as required" with no rates.
• A large deposit, or a discount for paying cash.
• Pressure to sign today because a "slot has come up" or materials are about to go up.
• No mention of Building Control, or an offer to "do it without".
• Exclusions you only find out about when you ask.
• A price wildly below every other quote you have. A builder who is 30% cheaper than three others has usually missed something — and will want paying for it later.

A checklist to run against every quote

1. Is it a fixed quotation or an estimate?
2. Is VAT included, and is the VAT number real?
3. What is excluded, in writing?
4. What are the provisional and prime cost sums, and are they realistic for what you want?
5. Are scaffolding, skips and making good included?
6. Who applies for Building Control, and who pays the fee?
7. What is the deposit, and how are later payments worked out?
8. How are variations priced and agreed?
9. What is the programme, and what happens if it slips?
10. What guarantee is offered on workmanship, and is there insurance behind it?
11. Is there a written contract, and have you read it?

If you want help with the rest of the conversation, our guide to the questions to ask a builder before you sign picks up where this one leaves off.

Questions people ask about builders' quotes

Where these facts come from

• Consumer Rights Act 2015 — sections 49 to 52 on services: care and skill, price, time.
• Consumer Contracts (Information, Cancellation and Additional Charges) Regulations 2013 — the 14-day cancellation period.
• GOV.UK: when to register for VAT — the £90,000 threshold.
• HSE: CDM 2015 and domestic clients.
• Citizens Advice: before you get building work done — quotes, deposits, payment methods and warning signs.
• JCT Home Owner contracts.

This is a builder writing, not a solicitor. For a contract with serious money in it, take proper advice before you sign.