How Many Quotes Should I Get for an Extension? At Least 3 - Here's Why

You're planning an extension and you know you need quotes. But how many? One feels risky. Ten feels excessive. And you've already spent two weeks trying to get a single builder to return your call.

Short answer: get at least three. Ideally five. And here's the part most people miss - the number matters less than what you do with them.

Why one quote is never enough

With a single quote, you have no frame of reference. The builder says £65,000. Is that fair? Cheap? Outrageous? You genuinely cannot tell.

It's like someone offering to sell you a car for £18,000 when you've never bought a car before and have no idea what they normally cost. You'd check, wouldn't you? Same principle.

One quote gives you a number. Three quotes give you a range. Five quotes give you a market.

Why three is the minimum

Three quotes let you do something crucial: spot the pattern.

If all three come in between £58,000 and £67,000, you know the market rate for your project. If one's at £85,000 and the other two are at £62,000, you know someone's either included more or is taking the piss. If one's at £42,000 and the others are at £65,000, that cheap quote almost certainly has gaps. The builder has either misunderstood the scope or left things out deliberately.

Three quotes also let you compare approach, not just price. Builder A might suggest steel beams where Builder B suggests timber. Builder C might include underfloor heating as standard while the others list it as an extra. Those differences tell you who's thought carefully about your project and who's just punched numbers into a spreadsheet.

Why five is better

Five quotes give you statistical confidence. With three, one outlier can skew your perception. With five, the pattern is clearer.

You'll typically see quotes cluster into a band - say, £60,000–£72,000 - with maybe one above and one below. That cluster is your market rate. Anything significantly outside it needs explaining.

Five quotes also mean you've met five builders. You've had five conversations about your project. By the fifth, you'll know more about extensions than you did after the first. You'll ask better questions. You'll spot things you missed earlier. That knowledge is worth the time.

The cheapest quote is often the most dangerous

This catches people out constantly. You get five quotes. Four are between £62,000 and £71,000. One comes in at £48,000. Your brain screams: "Pick that one! Save twenty grand!"

Don't.

A quote that's 25–30% below the others almost always means something's missing. The builder might have:

• Excluded items the others included. Scaffolding, skip hire, building regs fees, decoration - these can easily add up to £5,000–£10,000. Check the exclusions list carefully.

• Underspecified the materials. They've quoted for basic uPVC windows while the others have quoted aluminium. Laminate worktops instead of quartz. Builder-grade kitchen instead of the one you actually want.

• Underestimated the work. Some builders quote low to win the job, then hit you with variations once they're on site. That £48,000 quote becomes £65,000 by the time they've "discovered" all the extras.

• Planned to cut corners. Cheaper materials, fewer coats of paint, minimum-depth foundations, skipping the damp-proof membrane. You won't notice until it's too late.

The cheapest quote isn't a bargain. It's a gamble. And you're gambling with your home.

How to compare quotes like for like

Getting multiple quotes only works if you're comparing the same thing. If Builder A has quoted for a plastered shell and Builder B has quoted for a fully decorated extension with a kitchen, the totals are meaningless.

Here's how to make a fair comparison.

Use the same brief

Give every builder the same written brief. Include:

• Dimensions (or architectural drawings if you have them)
• What you want included - structure, first fix, second fix, decoration, kitchen, flooring
• Your preferred materials where you have a preference
• Whether it's supply-and-fit or fit-only for things like the kitchen

If each builder is working from the same information, the quotes should be comparable. If they're not, the differences are revealing.

Compare scope, not just price

Pull the quotes side by side and check each section. Does every quote include:

• Groundworks and foundations?
• Structural steel?
• Brickwork and roofing?
• Windows and doors (and what type)?
• Electrics and plumbing (first and second fix)?
• Plastering and decoration?
• Scaffolding and skip hire?
• Building regulations fees?

If one quote is missing scaffolding and another includes it, add the cost of scaffolding (£1,500–£3,000) to the first quote before comparing.

Check the exclusions

A good quote will tell you what's not included. A bad one will leave it vague - and then charge you later. If the exclusions list is missing or suspiciously short, ask the builder to clarify. Our post on signs your builder might be overcharging covers this in detail.

Look at the detail, not just the total

A £67,000 quote with line-by-line breakdowns, clear exclusions, and a payment schedule is worth more than a £58,000 quote that says "rear extension as discussed." The detail tells you the builder has actually thought about your project. Vague quotes lead to vague outcomes - and that usually means surprise price increases once work starts.

Get a baseline before you get quotes

Here's a trick that saves you time and stress. Before you approach a single builder, get a cost estimate from MyBuildAlly.

Enter your extension type, size, location, and spec. You'll get a ballpark figure based on current regional data. Not a quote - a benchmark.

Now when builders' quotes come in, you've got an anchor. If your estimate says a 20m² rear extension in your area should be £55,000–£70,000 and a builder quotes £48,000, you know to dig into what's missing. If they quote £90,000, you know to ask why.

That baseline turns you from someone guessing into someone who knows the numbers. Builders notice the difference.

Practical tips for getting quotes

Start early

Good builders are booked 2–4 months ahead. If you want work starting in June, approach builders in February or March. Leaving it late means you're choosing from whoever's available, not whoever's best.

Be organised

Have your drawings ready. Know your budget range. Write down what you want. The more prepared you are, the faster and more accurate the quotes will be. Builders respect homeowners who've done their homework.

Thinking about using a platform? Read our comparison of MyBuilder vs getting your own quotes.

Don't just pick from Google

Ask neighbours who've had work done. Check local Facebook groups. Look at Federation of Master Builders listings. Personal recommendations from people whose finished work you can actually see are worth more than any online review.

Follow up

If a builder hasn't sent their quote within two weeks of the site visit, chase them once. If they still don't deliver, move on. A builder who can't manage a quote won't manage your project. If they're stalling on putting their price in writing, read our guide on what to do when a builder won't give you a written quote.

Don't share other quotes

Never tell Builder B what Builder A quoted. You want independent assessments, not competitive undercutting. If a builder asks "what are the others charging?" just say "I'd prefer each quote to stand on its own merits."

What the spread tells you

Once you've got your quotes, the spread between them tells a story.

Tight cluster (within 10–15%): The market rate is clear. All the builders broadly agree on the cost. Pick the one whose quote is most detailed, whose communication has been best, and whose references check out.

One outlier high (30%+): Ask them to break it down. They might have included extras the others haven't. Or they might just be expensive. Check whether there's a good reason before dismissing them.

One outlier low (25%+): Almost certainly missing scope. Go through the quote line by line and compare against the others. What's not there?

Wide spread (40%+): The builders have interpreted your brief differently. Go back to each one and clarify the scope. You might need to issue a clearer brief and ask them to requote.

The bottom line

Three quotes is the minimum. Five is better. But the number only matters if you're comparing properly - same scope, same spec, line by line. Once you have your quotes, our complete method for comparing builder quotes walks you through a line-by-line comparison.

The cheapest quote is rarely the best value. The most expensive isn't automatically the best quality. What you're looking for is a fair price, a detailed scope, and a builder who communicates clearly.

Get your free MyBuildAlly estimate first so you know what the numbers should look like. Then go get your quotes. You'll be comparing from a position of knowledge, not hope.

Create your free account and start comparing quotes against regional benchmarks today.