How to Compare Builder Quotes and Avoid Costly Mistakes

Choosing a builder is a major decision, particularly when the project involves tens of thousands of pounds. Getting several quotes is a sensible starting point, but comparing them is not always straightforward.

One builder might quote £42,000, another £48,000 and a third £56,000 for what appears to be the same job. The difference could reflect labour costs, materials, experience or the way the work has been priced. It could also mean that one quote excludes work another has included.

The cheapest quote is not necessarily the cheapest project. Before appointing a contractor, you need to understand exactly what each price covers, what remains uncertain and what you may need to pay for separately.

The Federation of Master Builders (FMB) recommends comparing at least three detailed written quotations on a like-for-like basis. Here is how to do that properly.

1. Make sure every builder is pricing the same job

A fair comparison starts before the quotes arrive.

If each builder receives a different description of the work, they may make different assumptions about the materials, construction methods, finish and extent of the project. Their prices will then be difficult to compare.

Before requesting quotations, prepare as much information as possible, including:

• Architectural drawings or plans, where applicable.
• A clear description of the work required.
• The materials and finishes you expect.
• The fixtures and fittings you want included.
• Any known access restrictions or site issues.
• Your preferred timescale.
• Details of any work you intend to arrange separately.

For example, if you are planning a kitchen extension, specify whether the price should include the kitchen units, appliances, worktops, flooring, lighting and decoration. Otherwise, one builder may price a completed kitchen while another prices only the building work.

The FMB recommends providing the same brief, drawings, specification and information about materials and responsibilities to each builder. The more clearly the project is defined, the less room there is for different assumptions. Source: FMB builder-selection guide.

2. What should a builder's quote include?

A written quotation should make it clear what you are paying for and how the price has been calculated.

At a minimum, check that it identifies the agreed work, materials, total price and any exclusions. For larger projects, you should also understand the proposed programme, payment stages and arrangements for additional work.

Use the following checklist when reviewing each quotation.

These checks reflect the FMB's guidance on what homeowners should compare, alongside Citizens Advice's advice on obtaining quotations.

A quotation does not necessarily need to be a lengthy document, but it should be detailed enough for you to understand the agreed scope and identify what is missing.

3. Check what has been excluded

Exclusions are one of the main reasons apparently comparable quotations can differ.

A builder may reasonably exclude certain tasks if you have agreed to arrange them separately. Problems arise when those exclusions go unnoticed and the homeowner discovers additional costs after the project has started.

Depending on the project, check whether the quotation includes:

• Demolition and preparation.
• Foundations and drainage.
• Structural steel and associated installation.
• Scaffolding and access equipment.
• Electrical and plumbing work.
• Plastering and making good.
• Flooring and decoration.
• Kitchen or bathroom installation.
• Waste removal and skips.
• Landscaping and external repairs.
• Final connections, testing and commissioning where applicable.

Pay particular attention to phrases such as "by others", "client supply", "provisional" and "excluded".

Ask the builder to explain anything you do not understand. If you are expected to purchase materials separately, clarify which items, who installs them and whether the necessary labour is included.

The FMB specifically recommends checking exclusions, allowances, waste removal and responsibility for specialist trades when comparing quotations. Read the FMB's checklist.

Costs that commonly fall outside a quotation are covered in our guide to the hidden costs of home renovation.

4. Understand provisional sums and prime cost allowances

A quotation may contain allowances for work or materials that have not yet been fully specified. These figures need particular attention because the final cost may differ from the amount initially shown.

Provisional sums

A provisional sum is an allowance for work that cannot yet be fully described or accurately quantified. It might apply to drainage alterations where the extent of the work is not yet known, for example.

The Royal Institution of Chartered Surveyors (RICS) defines provisional sums within its New Rules of Measurement as amounts set aside for work that cannot be adequately described and quantified at the time of pricing.

The important point is that a provisional sum is not necessarily the final price for that work. Ask what the allowance covers, how the actual cost will be established and whether additional labour, overheads or profit are included.

Prime cost allowances

A prime cost sum, often shortened to PC sum, generally provides an allowance for supplying an item that has not yet been selected or fully priced, such as tiles, taps or door furniture.

RICS explains that a PC sum for materials or goods is a supply-only allowance. Installation and associated costs may therefore need to be accounted for separately. Source: RICS, New Rules of Measurement 2.

For example, a quotation might include an allowance for bathroom tiles but exclude the labour required to fit them. The final price will depend on the tiles selected and the installation costs.

Do not compare two headline prices without checking their allowances. A quote with a lower total may simply contain lower provisional sums or exclude costs that another builder has priced properly.

Ask for each allowance to be listed separately, with its assumptions and exclusions made clear.

5. Check whether VAT is included

Always establish whether the quoted total includes VAT. Otherwise, you could underestimate the amount you need to pay.

HMRC states that most building work on existing houses and flats by builders and similar trades is subject to the standard 20% VAT rate, although particular types of work qualify for exceptions or reduced rates under specific conditions. Read HMRC's guidance on VAT for builders.

For example, if the standard rate applies:

That is an £8,000 difference between the price before VAT and the amount payable.

When comparing quotes, put every figure on the same basis. If one builder includes VAT and another excludes it, the headline prices are not directly comparable.

If the VAT treatment is unclear, ask the contractor to explain which rate applies and why.

6. Why is one builder's quote much cheaper?

A lower quotation does not automatically mean a builder is inexperienced or unreliable. Contractors have different overheads, workloads, supply arrangements and ways of pricing projects.

However, a significant difference deserves investigation.

Consider the following possibilities:

Different materials: One builder may have allowed for standard windows and fittings, while another has priced premium products.

Missing work: The lower quote may exclude waste disposal, decoration, structural work or other tasks you assumed were included.

Different allowances: A builder may have priced a low provisional sum for work that remains uncertain.

Different assumptions: One contractor may expect you to arrange specialist trades, purchase materials or manage parts of the project yourself.

Different project timings: Contractors may have different availability or estimates of how long the work will take.

Citizens Advice advises homeowners to be cautious when a price is significantly below competing quotes, as it may reflect different work, insufficient experience or other concerns. It is a reason to investigate, not proof that something is wrong. Source: Citizens Advice.

Ask the builder to explain substantial differences and confirm the answer in writing. You may discover that the lower price offers genuine value, or that it does not cover everything you need.

7. A worked example: comparing two builder quotes

Consider a homeowner comparing two quotations for a renovation.

Both builders have priced the main construction work, but Builder A has excluded flooring and decoration, while Builder B has included them.

The following figures are illustrative, not typical market prices. Assume both quotations exclude VAT, the standard 20% rate applies and the flooring and decoration excluded by Builder A would cost £3,000 including any applicable VAT.

Builder A initially appears £6,000 cheaper. Once the excluded work is included, the difference falls to £4,200.

Builder A may still offer better value, but the homeowner now has a more accurate comparison.

The remaining questions concern the specification, workmanship, timescale, payment terms and reliability of each contractor.

This is why it is worth comparing the cost of the finished work you actually want, rather than simply choosing the lowest figure on the page.

8. Compare payment terms and timescales

Price is only one part of the agreement. You should also understand when the work can start, how long it is expected to take and when payments will be due.

Check whether the quotation includes a payment schedule and whether each payment relates to a defined part of the work. For larger projects, staged payments can provide a clearer structure than one large upfront payment or an unclear sequence of invoices.

The FMB recommends agreeing a written contract covering the work, price, timescale and payment schedule before construction begins. Its guidance also advises checking that the relevant stage has been completed before making each payment. Source: FMB.

For more on tying payments to completed stages, see how milestone payments protect homeowners.

Ask how the contractor will deal with unexpected work, changes to materials and delays. A variation should clearly record what is changing, the additional or reduced cost and any effect on the programme.

Do not rely on a verbal understanding that extra costs will be settled later.

9. Look beyond the price when choosing a builder

Once you have established which quotations are comparable, consider the contractor's suitability for the project.

Check their experience with similar work, ask to see recent projects and speak to previous customers where possible. Confirm that appropriate insurance is in place and verify any trade memberships or qualifications relevant to the work.

The FMB recommends checking references, relevant experience, insurance, communication and who will manage the project day to day. It also points out that there is no single licence required simply to call yourself a builder in the UK, so checking credentials matters. Read the FMB's builder-selection guide.

Our UK builder vetting checklist sets out the checks to make before you appoint a contractor.

Pay attention to how each contractor responds to questions. A builder who explains the quotation clearly and is open about uncertainties gives you a better basis for agreeing the work.

Finally, make sure there is a written contract before construction starts. The contract should reflect the accepted quotation and cover the scope, price, programme, payments, variations and how problems will be handled.

10. How Fort helps you manage the agreement

Comparing quotations helps you choose a builder, but keeping the project organised matters once the work starts.

Fort helps homeowners and contractors keep project details, documents, communications and agreed changes together in one place. You can post a project and connect with tradespeople on Fort, or invite a contractor you already know.

Once you have agreed the scope and price, Fort's project tools help keep the relevant information accessible as the work progresses. Changes can be recorded and approved, giving both parties a clearer reference point when the scope or cost needs to change.

Fortified milestone payments let homeowners and contractors agree defined stages of work, with funds secured before the stage begins and released when the agreed work is completed. This helps align payments with progress.

Fort does not replace a properly drafted contract or guarantee that a project will stay within budget. It provides a more organised way to manage the project information, variations and payment stages that support the agreement.

Whether you are planning an extension, a kitchen renovation or a larger refurbishment, find out how Fort helps homeowners manage construction projects.

Builder quote comparison checklist

Before appointing a contractor, make sure you can answer the following questions:

• Have all builders priced the same drawings and specification?
• Does each quotation list the included work and materials?
• Are exclusions clearly identified?
• Are provisional sums and prime cost allowances explained?
• Is VAT included, and has the applicable rate been confirmed?
• Have you considered the total cost of completing the project?
• Are the start date, duration and payment schedule clear?
• Is there a written process for approving variations?
• Have you checked the builder's experience, references and insurance?
• Are you ready to agree a written contract?

If several of these points remain unanswered, ask for clarification before choosing a contractor.

Frequently asked questions

How many builder quotes should I get?

The FMB recommends at least three detailed written quotations where practical. Comparing several quotes helps you understand the likely cost and identify differences in scope, allowances and proposed methods of working. Source: FMB.

Is the cheapest builder quote always the worst?

No. A lower quotation may represent good value if the scope, materials and standard of work meet your requirements. The important step is to understand why the quotes differ and whether any work or costs have been excluded.

What is the difference between a quote and an estimate?

A quotation is an offer to carry out specified work at an agreed price. An estimate is an approximation of the likely cost. Citizens Advice explains that a trader generally cannot simply increase an agreed quoted price without a valid reason, such as additional work that the customer has agreed to pay for. Source: Citizens Advice.

What is a provisional sum in building work?

A provisional sum is an allowance for work that cannot yet be fully described or accurately quantified. The final amount may differ once the work is defined and priced. Ask what the allowance includes and how any difference will be calculated. Source: RICS.

Should I sign a contract after accepting a builder's quote?

Yes. A written contract should set out the agreed scope, price, timescale, payment schedule, responsibilities and process for changes. It provides a shared record of what both parties have agreed before work begins. Source: FMB.

Final thoughts

Comparing builder quotes properly takes more than looking at the total price. You need to understand what each contractor is offering, what is excluded, which costs remain uncertain and how the work will be managed and paid for.

Obtain detailed written quotations, compare them on the same basis and ask questions whenever something is unclear. Check the contractor's experience and insurance, and agree a written contract before work starts.

A well-priced project is one where you understand what you are paying for and have a clear agreement about what happens if the work changes.

Choose your builder with confidence, then keep the project organised with Fort.

Explore Fort for homeowners.

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Sources and further guidance

• Federation of Master Builders: How to choose a trusted builder
• Citizens Advice: Before you get work done on your home
• Citizens Advice: Problems with building work, decorating or home improvements
• RICS: New Rules of Measurement 2, detailed measurement for building works
• HMRC: VAT for builders
• Fort: How to vet a builder before hiring
• Fort: How milestone payments protect homeowners during renovations

This article provides general information for homeowners. Requirements and consumer rights can vary across the UK. Check the relevant guidance for your nation and seek professional advice for your specific project where necessary.