Why Are Builder Quotes So Different? (And How to Compare Them Fairly)

You asked three builders to price the same job. You gave them the same drawings and showed them round the same house. And the quotes have come back thousands of pounds apart, sometimes tens of thousands.

It's one of the most common things people send me, and it's unsettling. Is the cheap one cutting corners? Is the expensive one taking you for a ride? Is the middle one safe?

Usually, none of the above. In my experience, when quotes are far apart it's almost never because one builder is honest and the others aren't. It's because they haven't priced the same job. Once you know where the gaps come from, you can compare them properly and pick the one that's actually the best value.

Quick answer

Builder quotes for the same job differ because builders:

1. Price different scopes, with different things included and excluded
2. Assume different specifications where the drawings don't say
3. Handle unknowns differently, using provisional sums, PC sums and risk allowances
4. Treat preliminaries differently (scaffold, skips, welfare, supervision)
5. Sit on different sides of the VAT line
6. Have different overheads, ways of working and workloads
7. Sometimes simply make mistakes or misread the drawings

The first five are about what is being priced. Sort those out and the gap usually shrinks a lot. What's left is the genuine difference in price between builders.

1. They've priced different scopes

This is the big one. One builder's price takes you to finished decoration. Another stops at bare plaster. One includes the kitchen fit, another assumes your kitchen company does it. One includes making good after the electrician, another doesn't mention it.

The exclusions list (if there is one) is often where the difference lives. Common items that are in one quote and missing from another include:

• Decorating and floor finishes
• Making good after electrics and plumbing
• Kitchen or bathroom fitting (as opposed to the building work around them)
• Drainage alterations
• Structural steel, padstones and fire protection
• Garden, path or driveway reinstatement
• Building control fees and the structural engineer
• Skips, scaffold and waste removal

A quote that's missing a few of these isn't cheaper. It's just shorter.

2. The drawings don't say everything

Architect's drawings show walls, windows and the roof. They usually don't tell a builder what kind of doors you want, how many sockets, what flooring, which tiles, whether the downlights are basic or fire-rated, or what level of finish you expect.

So each builder fills the gaps with their own assumptions. One prices standard uPVC doors, another prices aluminium bi-folds. On a typical extension, the glazing alone can swing the price a long way. That's why our guide to checking a builder's quote puts so much weight on a written specification.

The fix: give every builder the same drawings and the same written specification or schedule of works, so they're all pricing the same finished result.

3. They've handled the unknowns differently

Some things can't be priced exactly until work starts: how deep the foundations need to go, what's behind the plaster, whether the drains are where the drawings say. Builders deal with this in different ways:

• A provisional sum: an allowance for work that can't be priced yet, for example "drainage alterations, provisional sum £2,000". The final cost could be more or less.
• A PC (prime cost) sum: an allowance for something you haven't chosen yet, such as tiles, sanitaryware or a kitchen.
• Pricing the risk in: some builders don't use allowances. They put a fixed price on it that includes their own guess at the worst case.

A builder who wants to look cheap can set allowances low. The quote looks good, then the real cost lands later. A builder who prices the risk in looks expensive on paper but may cost you less in the end. Add up the provisional and PC sums in each quote and ask whether each one is realistic. A quote that's largely provisional isn't really a fixed price at all.

4. Preliminaries are shown, hidden or missing

Preliminaries are the cost of running the site: scaffold, skips, welfare, protection, insurance and supervision. One builder lists them clearly. Another spreads them through the other prices. A third leaves them out, or writes "scaffolding by others".

If you only compare totals, the builder who left them out looks cheapest. Read our guide to preliminaries in a builder's quote for what should be in there.

5. VAT

A builder must register for VAT once their taxable turnover goes over £90,000 in a 12-month period (GOV.UK). Smaller builders under the threshold don't charge it. Larger firms add VAT at the standard 20% rate on most building work to existing homes.

So two builders could charge the same amount for the work, but if one is VAT registered and one isn't, the totals you pay will be 20% apart. Also check whether each quote says "plus VAT" or "including VAT". It's easy to compare a VAT-inclusive total with a VAT-exclusive one without noticing.

The fix: turn every quote into the total you'll actually pay, including VAT, before you compare.

(If you're renovating a home that's been empty for two years or more, a reduced 5% rate may apply. See our guide to 5% VAT on empty home renovations.)

6. Different builders, different costs

Once the scope is the same, there's still a genuine difference between builders. That's normal. It comes from things like:

• Overheads: a firm with a yard, vans, office staff and a site manager costs more to run than a builder working from home with a small team. You may get more organisation for that money.
• Employed staff or subcontractors: builders who use their own trades often price differently from those who subcontract most of the work.
• How busy they are: a builder with a full diary may price high. Some will tell you honestly that they'd only do it at that price.
• Their reading of the risk: an older house, tight access, a party wall or an awkward neighbour all make some builders add more margin than others.
• Access and logistics: everything coming through the house in a mid-terrace costs more labour than a wide side access, and some builders price that in more carefully.

7. Mistakes

Builders are human. Someone misreads a drawing, misses a page, or prices a single-storey roof on a double-storey extension. Under-pricing by mistake is one of the riskiest outcomes for you. A builder who realises halfway through that they're losing money on your job is not in a good place, and neither are you.

Is the cheapest quote a red flag?

Not always. But when one quote is a lot lower than the others, I'd want to know why before you go anywhere near a deposit. Citizens Advice makes the same point: a much lower price might mean the trader isn't quoting for exactly the same work (Citizens Advice).

Ask the cheapest builder, politely and in writing: "Your price is quite a bit lower than the others. Could you talk me through what's included, so I know I'm comparing like with like?" A good builder won't be offended. Watch out if the answer is vague, like "we're just more efficient", or if the reply comes with pressure to sign quickly.

And the most expensive quote isn't automatically the safest. Sometimes it's the one that's priced the job properly. Sometimes it's a builder who doesn't really want it.

How to compare builder quotes like for like

Here's the process I use when someone sends me three quotes.

Step 1: Turn every quote into a VAT-inclusive total

Write down what you'd actually pay for each one.

Step 2: Make a scope table

Put the main parts of the job down the side and the builders across the top. Mark each cell Included, Excluded, Provisional (£) or Not mentioned.

Illustrative example only, not a real job.

Step 3: Price the gaps

For every "Excluded" or "Not mentioned" item, ask that builder to price it, or get a rough figure elsewhere and add it to that quote. Treat "Not mentioned" as "Excluded" until the builder confirms it in writing.

Step 4: Look hard at provisional sums

Add them up for each quote. Ask each builder how they arrived at each figure and what happens if the real cost is higher.

Step 5: Compare the adjusted totals, then the terms

Only now compare prices. Then look at the things that affect your risk: the deposit (I'd normally expect 5-10%), whether payments are tied to finished stages of work, the programme, insurance and warranty. Our article on stage payments explains what a fair schedule looks like.

Step 6: Send each builder the same questions

Any differences you still can't explain, ask about. Use the same email for each builder so the answers are comparable.

Our free builder quote comparison tool walks you through this side by side for up to three quotes. If you only have one quote so far, start with the builder quote checker.

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Questions to ask every builder

1. Which drawings, revision numbers and documents have you priced from?
2. What's excluded from your price?
3. Which items are provisional or PC sums, and how did you arrive at each figure?
4. Are scaffold, skips, waste removal and protection included?
5. Is the price including or excluding VAT? Are you VAT registered?
6. Who pays for building control, the structural engineer and any party wall costs?
7. What specification have you assumed for doors, windows, flooring and electrics?
8. Does your price include making good and decorating?
9. How long will the job take, and what is the payment schedule?
10. How will any changes be priced and agreed?

The short version

Big differences between builder quotes are normal, and they're rarely about honesty. They come from different scopes, different assumptions, different handling of unknowns, prelims and VAT. Put every quote on the same footing first: VAT-inclusive, same scope, gaps priced, provisional sums checked. What's left is the real difference, and that's the one worth paying attention to.

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More in this quote series: VAT on a builder's quote · provisional and PC sums · schedule of works template · can a builder charge more than the quote · day rate vs fixed price.