My Builder Changed the Price After Starting - What Can I Do?
If your builder has increased the price after work started, here's what's legitimate, what's not, and what the law says you can do about it.
It's one of the most stressful things that can happen mid-build. You agreed a price. Work started. And now your builder says it's going to cost more. Maybe a lot more.
First things first: don't panic, and don't agree to anything on the spot. You have rights here. But what you can do depends on why the price has changed and what was agreed at the start.
Let's untangle it.
Three reasons a price might change mid-project
Not all price increases are dodgy. But not all of them are legitimate either. Here are the three scenarios you're likely dealing with.
1. Genuine unforeseen problems
Your builder opens up a wall and finds the timber frame behind it is rotten. They dig the foundations and hit an old drain nobody knew about. They strip the roof and discover the rafters need replacing.
These things happen. Older properties especially are full of surprises. A builder can't price for problems they didn't know existed - and if the original quote was based on what was visible at the time, an increase to cover genuinely unexpected work can be reasonable.
Key test: Was this something the builder could reasonably have known about before starting? If the answer is no, a variation (a formal change to the agreed scope and price) is legitimate.
What's reasonable: The builder should tell you about the problem as soon as they find it. They should explain what needs doing, give you a written price for the extra work, and let you decide before they proceed. No surprises. No "I've already done it, here's the bill."
2. Scope creep - you asked for changes
You decided you wanted underfloor heating after all. Or you upgraded from laminate to engineered oak. Or you asked for an extra socket in the utility room and a different layout in the en-suite.
Each change is small. But they add up. And every change to the original scope is a legitimate reason for the price to increase.
Key test: Did you request changes after the quote was agreed? If so, the builder is entitled to charge for them.
What's reasonable: Each change should be priced separately, in writing, before the work is done. This is called a variation order. Good builders will issue one automatically. If yours doesn't, insist on it.
The problem arises when builders don't price variations upfront and instead lump them all together at the end as a surprise "extras" invoice. That's poor practice - and it's avoidable if you agree a process for handling changes at the start.
3. Dishonest price hiking
This is the one you're worried about. The builder quoted low to win the job, knowing they'd increase the price once you were committed. Or they "forgot" to include something obvious and are now charging for it as an extra.
Key test: Was the item clearly part of the original scope? If your quote says "supply and install rear extension as per drawings" and the builder is now saying plastering wasn't included - that's not a genuine variation. That's either incompetence or dishonesty.
What's not reasonable:
- "Materials have gone up since I quoted." Possible, but a fixed-price quote means the builder absorbs that risk, not you. Unless the contract includes a materials escalation clause (rare in residential work), the original price stands.
- "It's taken longer than I expected." Same principle. A fixed-price quote means the builder wears the time risk. If they underestimated, that's their problem.
- "I didn't realise the job was this complicated." If they visited the site, saw the drawings, and wrote a detailed quote, they should have realised. Underquoting and then hiking the price is a textbook red flag - and one we cover in detail in signs your builder is overcharging.
What the law says
The Consumer Rights Act 2015 (the law that protects you when you pay someone for a service) is your main protection here. Our guide to consumer rights in building disputes covers the full legal framework, including what to do when things escalate.
In plain English, it says:
- The price you agreed is the price you pay. If you agreed £60,000 for an extension, the builder can't unilaterally change it to £68,000. Any price change needs your agreement.
- The work must be done with reasonable care and skill. If the builder made an error in their quote - missed something obvious, underestimated quantities - that's a failure of skill on their part, not your problem.
- The work must be done within a reasonable time. If the builder is dragging the job out and the delays are costing you money, you may have a claim for the additional costs.
Written contract vs verbal agreement
If you have a written contract with a fixed price, your position is strong. The price is documented. Any changes need to be agreed in writing.
If you don't have a written contract - maybe you agreed the price over the phone or in a quick email - you're still protected by the Consumer Rights Act. But proving what was agreed becomes harder. It's your word against theirs.
This is why getting everything in writing before work starts is so important. A quote isn't just a price - it's evidence of what was agreed. If your builder's quote is missing key details, our guide on what a builder's quote should include covers exactly what to look for.
Quote vs estimate - a critical difference
A quote is a fixed price for a defined scope of work. Once you accept it, the builder is bound by it (subject to agreed variations).
A estimate is a rough guide. It's not binding. The final price can differ.
If your builder gave you an estimate rather than a quote, they have more room to adjust the price. This is why you should always insist on a written, fixed-price quote - not an estimate.
Check your paperwork. Does it say "quotation" or "estimate"? That one word makes a big legal difference.
What to do right now
If your builder has just told you the price is going up, here's your step-by-step plan.
Step 1: Don't agree on the spot
Say: "I need to see that in writing before I can agree to anything." This isn't rude. It's sensible. Any builder who pressures you into agreeing to extra costs verbally, on the spot, is not acting in your interests.
Step 2: Get the variation in writing
Ask the builder to put the proposed change in writing. It should include:
- What the extra work involves
- Why it's needed (unforeseen problem, your requested change, or something else)
- The additional cost, broken down into labour and materials
- How it affects the timeline
If they won't put it in writing, that's a red flag.
Step 3: Check it against the original quote
Go back to your original quote. Is the "extra" work something that should have been included? For example, if the quote says "full bathroom installation" and the builder is now charging extra for tiling - tiling is part of a full bathroom installation. Push back.
If you're not sure what should have been included, upload your quote to MyBuildAlly and we'll flag any gaps in the scope that might lead to surprise extras later.
Step 4: Get a second opinion on the cost
If the variation seems legitimate but the price feels steep, ask another builder or tradesperson for a rough price on the same work. A five-minute phone call can tell you whether £3,500 to replace rotten joists is fair or inflated.
Step 5: Negotiate if needed
You don't have to accept the first price. If the variation is legitimate but the cost is too high, say so. "I understand this needs doing, but £4,000 seems high for two days' work. Can you break down the labour and materials?"
A good builder will work with you. A defensive one is telling you something.
Step 6: If it's not legitimate, push back firmly
If the builder is trying to charge for work that was clearly in the original scope, say so in writing. Reference the original quote and the specific line item. Keep it factual, not emotional.
If they won't back down, you have options:
- Mediation. Citizens Advice can direct you to free mediation services for consumer disputes.
- Trading Standards. If the builder is acting dishonestly, report them to your local Trading Standards office.
- Small claims court. For disputes under £10,000, the small claims process is designed for exactly this kind of disagreement. You don't need a solicitor.
How to prevent this next time
The best way to handle mid-project price increases is to make sure they can't happen without your agreement.
- Get a detailed, fixed-price quote. Not an estimate. Not a lump sum. A line-by-line breakdown with a fixed total. If you're not sure whether your quote is detailed enough, check it against our post on how to read a builder's quote.
- Use a written contract. The JCT Minor Works contract or the FMB homeowner contract both include clear processes for handling variations. Our guide to building contracts for homeowners compares the options and explains what each one covers. They're under £50 and worth every penny.
- Agree a variation process upfront. Before work starts, agree that any changes to scope or price must be put in writing, priced, and approved by you before the work is done. No verbal agreements. No retrospective invoices.
- Include a contingency. Budget 10–15% above the quoted price for genuine unforeseen issues. That way, if problems do crop up, you've got a financial buffer and you're not making decisions under pressure.
- Keep a project diary. Note down what's agreed, when, and with whom. If a dispute arises, contemporaneous notes (notes made at the time, not written up later) carry a lot of weight.
- Check your quote isn't missing key items. Missing items are the number one cause of mid-project price increases. Things like building regulations fees, scaffolding, and skip hire should all be mentioned - either as included or excluded. If they're not there, ask before work starts.
- Agree payment terms that protect you. Stage payments tied to milestones keep the builder incentivised and limit your exposure. If your builder's asking for a large chunk upfront, read our post on whether a 50% deposit is normal before you hand anything over.
If your builder's asking for more money and you're not sure whether it's fair, you don't have to figure it out alone. Run your quote through MyBuildAlly to see how it stacks up against regional benchmarks - and whether anything's missing that might cause problems down the line.
The bottom line
A price change isn't always a scam. Sometimes genuine problems crop up and extra work is needed. That's building.
But the process matters. You should always be told about changes before they happen. You should always see the cost in writing. And you should always have the chance to say no.
If that's not happening, something's wrong - and you have every right to push back.