Is My Builder Ripping Me Off? How to Tell an Overcharge From a Missing Item

You are eleven weeks into a project you were told would take eight. The bill has passed the number on the quote and it is still moving. Nobody has done anything you can point at and call dishonest, but you have started counting the vans on the drive and you no longer look forward to Monday morning.

So you type the question into your phone at half past eleven at night: is my builder ripping me off?

Here is the honest answer, from builders who read other builders' quotes for a living. Usually, no. In most jobs that end up in this state, nobody set out to cheat anybody. The quote was incomplete, both sides read the gap differently, and the difference landed on the homeowner three months later when there was no leverage left. That is not fraud. It is worse in one specific way — it is entirely preventable, and it destroys the working relationship just as thoroughly.

This guide is about telling the two apart, because the response is completely different. Being overcharged is a dispute. Being under-quoted is a budgeting failure that you can still get in front of.

Quick answer: is my builder ripping me off? Most price rises on UK domestic building jobs are not overcharging — they are work that was never in the original quote. Ask for the original quote, the specification it priced, and every variation in writing side by side. If the extra work appears in none of them, it is a genuine addition and you owe it. If it appears in the original scope, you have already paid for it. Real quotes for the same extension routinely vary by 40%, almost always because of what each builder excluded rather than what each charges per day. A single-storey extension costs £1,900–£2,700 per square metre in the UK in 2026, so a 20m² rear extension runs £50,000–£80,000 all-in outside London and £65,000–£105,000 inside the M25 — if your all-in figure is well under that, the shortfall is missing scope, not a bargain.

The three reasons your bill went up

Every overrun on a domestic job comes down to one of three things. Before you accuse anyone of anything, work out which one you are looking at.

1. You changed something. You moved a door, upgraded the tiles, added sockets, decided the island should be bigger. Each of these felt small in the moment and was probably agreed on site in ninety seconds. They are legitimately chargeable, and this is the most common cause of an overrun by a wide margin.

2. It was never in the quote. Scaffolding, waste removal, decorating, building control fees, the structural engineer, making good the garden. The builder never included it, never said so out loud, and you assumed it was covered because the quote said "extension". This is the second most common cause, and it is the one that generates the most bad feeling — because both parties genuinely believe they are in the right.

3. You are actually being overcharged. The rate went up mid-job without agreement. Provisional sums were spent with no invoices. Day-work is being billed for men who were on someone else's job. This is the rarest of the three, and it looks different from the other two — which is the point of the rest of this guide.

The test is documentary, not emotional. Put three things on the table: the original quote, the drawings and specification it was priced against, and every variation agreed since. If the disputed item does not appear in any of them, it is category two — a genuine addition that was never priced, and you owe something for it even though it should have been flagged. If it appears in the original scope and you are being asked to pay again, that is category three, and you should stop paying and get advice.

Why this poisons the relationship, and why that costs you money

The moment a homeowner starts suspecting they are being fleeced, three things happen, all of them expensive.

The homeowner starts scrutinising everything, including things that are perfectly normal. The builder — who in most cases is not cheating anybody — feels accused, and gets defensive. And the relationship shifts from two people solving problems together to two people building a case.

That shift costs real money. A builder who feels trusted will absorb small things, flag problems early, and suggest the cheaper way of doing something. A builder who feels accused will price every variation defensively, put everything in writing to protect himself, do exactly what the drawing says and nothing more, and stop volunteering the fact that the thing you have chosen is going to look wrong.

The irony is that the homeowner's suspicion, which was triggered by an incomplete quote, ends up costing more than the incomplete quote did.

The fix is not to trust blindly. It is to move the argument off the personalities and onto the paperwork. "I want to understand where this is coming from — can we go through the original scope together" is a completely different conversation from "I think you are taking me for a ride." It gets you the same information and it leaves you with a builder who still wants to do a good job.

The items that are almost never in the quote

This is where the money goes. Below are the things we most often find missing when we review a quote — and the ranges we would expect them to add. If your quote does not mention an item on this list, assume it is excluded until the builder confirms in writing that it is not.

Commonly missing item	Typical cost to add	Why it gets left out
Structural engineer's design and calculations	Part of the 9–14% professional fees	Builder assumes the architect arranged it
Building control application and inspections	Several hundred to low four figures	Genuinely ambiguous who applies
Planning or lawful development application	A few hundred pounds plus drawings	Usually the homeowner's, but nobody says so
Party wall surveyors	£1,200–£3,500	Only becomes necessary once neighbours object
Structural steel and load-bearing openings	£2,200–£6,500	Priced as "provisional" pending engineer
Deep or stepped foundations	£200–£450 per m²	Depth unknown until the hole is dug
Drain diversion or building over a sewer	£900–£4,000	Not discovered until excavation
Kitchen supply and fit	£9,000–£22,000 mid-range	Builder prices installation only, not units
Glazing above the base allowance	£1,400–£18,000 depending on the doors	The single widest variable in an extension
Rooflights and lanterns	£1,400–£11,000	Assumed to be a client choice
Scaffolding, skips and skip permits	Varies by job	Bundled as "preliminaries" or dropped entirely
Decorating and floor finishes	Varies by job	Quote often stops at bare plaster
Garden and driveway reinstatement	£1,500–£6,000	Considered outside the works
Temporary accommodation or storage	Varies	Never the builder's problem
Contingency	10% of build cost, 15% for pre-war	Builders rarely quote it; you should hold it

Two of these deserve special attention because they cause more arguments than everything else combined.

Glazing. The difference between the standard windows in a base quote and a five-panel bi-fold across the back of the room is up to £10,500, and up to £18,000 for a slim-frame aluminium slider. If your quote says "glazing to rear elevation" with no make, model or panel configuration, you do not have a price — you have a placeholder.

Provisional sums. A provisional sum is an admission that the work cannot be priced yet. It is not a cap and it is not a promise. A quote of £68,000 with £14,000 of provisional sums is not a £68,000 quote, and the builder who wins the job on that number is not necessarily the one who will finish it cheapest. Ask, for every provisional sum: why can this not be priced now, what assumption sits behind the figure, will I see the supplier's invoices, and does your margin get added on top?

How to check whether the price itself is fair

Separately from what is missing, you can sanity-check the rate. Work out the all-in cost per square metre and compare it against what the work actually costs in 2026.

For a single-storey extension, £1,900–£2,700 per m² is the national range for a good-quality finish. Builder's standard specification comes in around 12% below that; a high specification runs about 28% above. Double-storey is roughly 10–15% cheaper per m² than single-storey, because the foundations and roof are shared across two floors. Then apply your region: London ×1.25, South East ×1.12, South West and East of England ×1.03, Midlands ×0.97, North of England and Wales ×0.92, Scotland ×0.95, Northern Ireland ×0.85. Access matters too — if everything has to come through the house rather than down a side passage, add about 12%.

On top of the build cost, expect professional fees of 9–14% and a contingency of 10%, or 15% on anything pre-war.

Run your own numbers through the extension cost calculator, or the loft conversion, kitchen, bathroom or whole-house renovation versions. Every rate is published on the page — you can read the full rate card without touching a slider.

If your quote lands inside the range, the price is not the problem and you should be looking at scope. If it lands well below, that is the clearest possible signal that something has been left out. A quote substantially cheaper than every other is almost always missing scope rather than being competitive.

What an actual rip-off looks like

Category three is rare, but it exists, and it does not look like a big final bill. It looks like these:

• The deposit was front-loaded. A sensible deposit is 5–10% on a mid-size or major job, up to 10–20% on something small. Above 25% before materials arrive on site is the most common single feature of domestic jobs that go wrong.
• Payments are tied to dates rather than completed work. Stage payments should follow verified milestones — foundations inspected, walls to damp-proof course, roof watertight, first fix complete — not the calendar.
• You are being asked to pay ahead of the stage. Paying for work that has not been done removes every piece of leverage you have.
• Cash is being pushed. No invoice, no paper trail, no VAT, no recourse, and no warranty worth anything.
• Provisional sums are being spent with no invoices produced. You are entitled to see what was actually bought.
• The same work is being charged twice — once in the original scope, once as a variation.
• Rates changed mid-job without agreement, or day-work appears for days you know the team was elsewhere.
• Variations are being priced after the work is done rather than before, so you never get the chance to say no.
• The builder will not put anything in writing. This is the strongest single signal on the list.
• There is no retention. You should be holding 5% for 3–6 months after practical completion on a major job.

Any one of these on its own deserves a question rather than an accusation. Three or more together, and you should stop the next payment and get independent advice before you release another penny. Our builder quote red flags guide goes through the warning signs in more depth, the complete guide to checking a builder's quote walks through every section a quote should contain, and the stage payments guide sets out what a safe schedule actually looks like.

How to raise it without wrecking the relationship

You still need this person to finish your house. Here is how to have the conversation.

Do it in person, not by text. A message reading "why is this so expensive" at 11pm lands as an accusation no matter how it was meant. Ask for twenty minutes on site.

Lead with the document, not the feeling. "I want to make sure I have understood the scope" gets you further than "I feel like I am being overcharged," and it gets you the same answer.

Ask for a running total, not a justification. The single most useful question is: what do you expect the final figure to be, including everything we have agreed since the quote? A builder who can answer that in a week is in control of your job. One who cannot, is not — and that is worth knowing regardless of anyone's honesty.

Ask for the variations in writing, retrospectively if necessary. "Can you send me a list of everything that has been added since the original quote, with a price against each" is a completely reasonable request and no honest builder will object to it.

Fix the process from here. Agree that from today, nothing gets done until it is priced and confirmed by email. This costs the builder nothing and it stops the bleeding immediately.

Do not stop paying for completed work. If you genuinely believe you are being overcharged, withhold the disputed amount and pay the rest, in writing, with the reason stated. Stopping everything turns a disagreement into a legal problem.

Get a third party to look at it. This is the part that defuses it. When an independent builder reads the quote and says "the steel was never in there, that is a legitimate extra" — or "that was in the original scope, you have paid for it once already" — the argument stops being your word against his.

The checklist: are you about to overspend?

Print this and work through it before you sign anything, or tonight if you are already underway.

The quote itself

• It says quotation, not estimate, and the wording states which parts are fixed
• It names the drawings and specification it was priced against, by revision
• Every builder who quoted received exactly the same documents
• The work is broken down by trade or stage, not presented as one figure
• Materials are named — makes, models, thicknesses, not "quality uPVC"
• Glazing is specified by panel configuration and manufacturer
• There is a written exclusions list, and you have read it
• Every provisional sum is identified, with the assumption behind it
• VAT is stated, and stated as included or excluded
• The company name, address and VAT number are on the document

The money

• You have costed every exclusion and added it to your own budget
• The all-in figure per m² sits inside the published range for your region
• The deposit is 5–10% on a mid-size or major job
• Stage payments are tied to completed, inspected work — not dates
• A 5% retention is held for 3–6 months after completion
• You are holding a 10% contingency, 15% if the property is pre-war
• Professional fees of 9–14% are budgeted, whoever pays them
• Nothing is being paid in cash

The process

• Variations must be priced and agreed in writing before work starts
• You have agreed who applies for building control, and who pays
• Party wall position is resolved, and surveyors' fees are budgeted
• Start date and duration are stated, with what happens if it overruns
• Public liability and contract works insurance certificates seen and in date
• You know who provides electrical, gas and building control certificates
• You have called three references from jobs finished in the last year
• Companies House checked, and the trading name matches the bank details

If you are already underway

• You have a written list of every variation agreed to date, with prices
• You have asked for, and received, an expected final figure
• You have invoices for every provisional sum spent so far
• Nothing has been paid ahead of the stage it relates to
• The disputed amount, if any, is separated from the undisputed amount

If you can tick every line, you are very unlikely to be either overcharged or blindsided. If you cannot tick more than half of them, the risk is not that your builder is dishonest — it is that neither of you knows what this job actually costs yet.

Run the free builder quote checker for a structured version of the same test. No sign-up, no email capture.

Or send it to us and stop guessing

Working through that list alone, at eleven at night, on a document written in a trade's shorthand, is not a fair fight. It is what we do all day.

Send us the quotation, the drawings, the specification and whatever is bothering you. One consultation is £59 — a one-to-one call with a working UK builder plus a written report, within 24 hours and usually much faster. It tells you:

• What the quote actually includes, in plain English
• Which items are missing and what they will cost when they land
• Whether the allowances and provisional sums are realistic or optimistic
• Whether the price is reasonable for your region and this type of work
• Whether the payment structure puts you at risk
• The exact questions to put to your builder, and how to put them

We are independent builders. We are not bidding for your job, we do not take a fee from anyone quoting on it, and we have no interest in whether you proceed. There is a no-quibble money-back guarantee if the advice does not give you a clear answer.

Finding a missing £10,000 item before you sign is a great deal easier than discovering it in week eleven.