Estimate vs quote comes down to one thing: certainty on price. A quote is a fixed price for a clearly described job, and the builder can’t normally charge you more unless you agree to extra work. An estimate is the builder’s best guess, and the final bill can be higher. For a loft conversion or extension, always ask for a written, itemised quote.
We rarely give estimates. Before we price a loft, we survey it, measure it and work out the job stage by stage, so the quote we give is the price you pay. Where something genuinely can’t be known until work starts, we say so in writing, with the assumption we’ve made. This guide explains the estimate vs quote difference, what a good quote should include, why prices sometimes change, and your rights if the bill goes up.
Estimate vs quote at a glance
Builders use several terms for a price, and they don’t all mean the same thing.
| Term | What it means | Can the price go up? |
|---|---|---|
| Estimate | The builder’s best guess at the cost, often given quickly after a short visit. | Yes. The final bill should be reasonable, but it isn’t fixed. |
| Quote (quotation) | A price for a clearly described piece of work. | Not normally, unless you agree to extra work or the quote contains an obvious mistake. |
| Fixed price | A quote that’s agreed in the contract as the total for the work described. | Only for changes you ask for, or for assumptions stated in writing that turn out to be wrong. |
| Provisional sum | An allowance inside a quote for something that can’t be priced yet, such as unknown foundations. | Yes, up or down, once the real cost is known. |
| Prime cost (PC) sum | An allowance for items you’ll choose later, such as a bathroom suite or tiles. | Yes, depending on what you choose. |
So when you compare an estimate vs quote, remember that a low estimate isn’t a promise. A slightly higher quote with everything included will often cost you less in the end.
What a good building quote should include
A proper quote is a document, not a number scribbled on a notepad or sent by text. For a loft conversion, it should include:
- A description of the work, based on the drawings and specification. Good loft conversion plans make quotes far easier to compare.
- An itemised breakdown by stage (scaffolding, structure, roof, insulation, stairs, electrics, plumbing, plastering, decorating) and the main materials.
- What’s included and what isn’t, in writing.
- Any provisional or prime cost sums, with realistic amounts.
- Any assumptions, for example “assumes existing foundations are adequate, subject to trial pit”.
- VAT, clearly shown as included or extra.
- The payment schedule, tied to stages of work.
- A start date, timescale and how long the quote is valid.
What’s often left out of a cheap price
These are the items that turn a low price into a high bill:
- Architect and structural engineer fees
- Planning and Building Control fees
- Party wall surveyor costs (see our party wall guide)
- Scaffolding and skips
- Fire doors and smoke alarms required by the Building Regulations
- Moving water tanks or upgrading the boiler
- Decorating and making good below the loft
- VAT
The quality of the quote also tells you how the builder will run the job. A price given without measurements, notes or photos is a guess, however confident it sounds.
Why the price can change, and your rights
Even with a fixed quote, the final price can legitimately change in a few situations:
- You change the work. Adding a rooflight, moving a wall or upgrading the bathroom is a variation. Always ask for the cost in writing before the work is done.
- Provisional sums are settled. An allowance for something unknown is replaced by the real cost.
- A stated assumption turns out to be wrong. For example, the trial pit shows deeper foundations are needed. A good builder adjusts only that item, not the whole price.
If you’re charged more than the quote
Citizens Advice says a trader generally can’t charge more than a quote unless you agreed to extra work or the quote had an obvious mistake. Rising costs for the builder after the quote don’t justify a higher price. If there’s no good reason for the increase, tell the builder in writing that you’ll pay the quoted amount.
If you’re charged more than an estimate
You can challenge a bill that’s much higher than the estimate. Under the Consumer Rights Act 2015, where a price isn’t fixed, you must pay a reasonable price. Look at the original estimate, any changes and the reasons for them, then tell the builder in writing what you think is reasonable.
The easiest way to avoid both situations is to get a written quote, a written contract, and agree every change in writing. Our guide on how to choose a builder covers contracts and payments in more detail. This is general guidance, not legal advice.
How to compare quotes for a loft conversion
- Get at least three written quotes, and give every builder the same drawings and specification.
- Line them up item by item. Put the quotes side by side and check each one covers the same stages and materials.
- Add in what’s missing. If one quote excludes scaffolding, fees or VAT, add a realistic figure before you compare totals.
- Check the provisional sums. A quote with unrealistically low allowances will grow later.
- Read the assumptions and exclusions. These tell you where the price could change.
- Be wary of a price far below the rest. Something has usually been left out, or corners will be cut. Our guide to loft conversion mistakes shows what that can cost.
- Judge the proposal, not just the price. A detailed, well-presented quote usually means a well-run job.
For typical prices by loft type, see our guide to the different types of loft conversion.
FAQs
What is the difference between an estimate and a quote?
A quote is a fixed price for a clearly described job; an estimate is the builder’s best guess and can go up. In the estimate vs quote choice, a quote gives you certainty on price.
Is a builder’s quote legally binding?
Once you accept it, a quote generally becomes part of your agreement, and the builder can’t normally charge more unless you agree to extra work or the quote contains an obvious mistake. A written contract gives you the clearest protection.
Can a builder charge more than the estimate?
Yes, but the final price must be reasonable. If the bill is much higher than the estimate without a good reason, you can challenge it in writing.
How long is a building quote valid for?
It depends on the builder; many quotes are valid for 30 to 90 days because material prices change. The validity period should be written on the quote.
What is a provisional sum in a quote?
An allowance for work that can’t be priced accurately yet, such as foundations or hidden structural repairs. It’s adjusted up or down when the real cost is known, so check the amount is realistic.
Should I always choose the cheapest quote?
No. Compare what each quote includes first. The cheapest quote often leaves out fees, scaffolding or VAT, or relies on low provisional sums that grow later.
Get a fixed quote for your loft conversion
We’ll survey your loft, measure it and give you one itemised, fixed price, with any assumptions written down, so you know exactly what you’re paying before work starts.
