Two documents can describe the same £40,000 extension and carry completely different legal weight. Knowing which you’re holding, and converting the wrong one into the right one, is a ten-minute job that protects the whole budget.
The short answer
- A quote is an offer to do defined work for a fixed price. When you accept it, in writing, verbally, or simply by letting the work start, a contract forms on those terms. The builder can’t lawfully charge more for the quoted scope; changes need your agreement as variations.
- An estimate is a professional guess at the likely cost. It is not an offer, so accepting it fixes nothing. The final bill can lawfully differ, though not without limit: as a consumer you’re protected by the Consumer Rights Act 2015, which says that where no price is fixed you pay only a reasonable price for the work actually done.
The label isn’t decisive on its own, a court looks at the substance. A detailed document with quantities, a total and “valid for 30 days” reads as a quote whatever it’s called; a round number scribbled after a ten-minute walk-round is an estimate even if headed “quotation”.
When exactly does a quote become binding?
Contract law needs offer, acceptance and consideration. In practice:
- The builder’s priced quote is the offer.
- Your “yes, go ahead”, email, text, signature, or agreeing a start date, is acceptance.
- The promised price and the promised work are the consideration.
From that moment both sides are bound: the builder to the scope at the price, you to pay it. This cuts both ways, cancelling after acceptance can leave you liable for the builder’s wasted costs, subject to the cooling-off rights that apply to contracts signed in your home.
Quotes usually state a validity window (14–30 days is typical, given material price movement). After it lapses, the offer dies; asking the builder to “honour” an old quote is a request, not a right.
What can a builder add to an accepted quote?
Only three things, legitimately:
- Agreed variations, you asked for changes, and the price for them was agreed (get it in writing before the work happens).
- Provisional sums being firmed up, if the quote said “allow £3,000 for the bathroom fittings”, the real figure replaces the allowance, up or down.
- Genuinely unforeseeable work, something no competent builder could have priced (hidden rot behind a wall). Even then, it should stop-and-be-priced, not appear on the final invoice.
What a builder cannot do is re-price quoted work because “materials went up” or “it took longer than we thought”, that risk is exactly what a fixed quote allocates to them. If it happens, our disputes guide covers the response; you generally owe the quoted price, not the inflated invoice.
What’s a “reasonable price” on an estimate?
Where only an estimate exists, courts ask what the work would ordinarily cost, trade rates, quantities, comparable jobs. As a working rule, a final bill within 10–15% of a written estimate rarely surprises anyone; beyond 30% the builder should have warned you as soon as the drift became apparent, and a court will scrutinise anything they didn’t flag. Benchmarks help you argue this: the UK Renovation Cost Index and trade day rates exist for exactly this comparison.
Protecting yourself in practice
- Ask for a quote, not an estimate, once the scope is defined, and get the scope defined first with a proper brief.
- Accept in writing, referencing the quote by date: “We accept your quotation of 14 March for £42,300 inc VAT.”
- Attach it to a contract. A quote fixes price; a contract fixes everything else, programme, payments, defects, disputes.
- Keep every revision. Requoted versions supersede each other; know which one you accepted.
This guide is general information for homeowners in England and Wales, not legal advice.
