Budget tool · Surrey home extensions
The builder's number isn't the project cost.
Most budgets cover the build and stop. Then contingency, VAT, the kitchen and the fees arrive, and the number you planned around has moved. Put in your floor area and see the whole figure, layer by layer.
Your budget, layer by layer
These are ranges, not prices. Surrey benchmarks, before VAT. Specification, site conditions and contingency of 10–15% all move the number. Kitchen and bathroom guide prices are typical UK figures for 2026, VAT included.
What real tenders came back at
From JWA's own tenders and estimates, 2025 and 2026, excluding VAT and rounded.
- Small single-storey extension, rewire, new heating and redecoration£125,000–£135,000
- Single-storey extension, loft conversion and refurbishmentabout £230,000
- Two-storey extension, garage conversion and refurbishment£330,000–£370,000
Where would your project really sit?
A range like this is a starting point. Your own figures depend on the house, the site and the order the decisions are made in. If you're weighing up an extension, the free 15-minute Clarity Call is a sensible first step.
How to read this
The range is wide on purpose. The low end assumes a straightforward house and a modest specification; the high end assumes the opposite. Most projects land somewhere between, and where yours lands depends far more on the decisions made early than on anything a calculator can see.
That is what the Clarity Pack is for: testing the layouts, the planning position, the structure and the cost bands against your own house before you commit to drawings or builders. For more on where the money goes, read what an extension costs in Surrey and extension costs explained.
How much does an extension cost in Surrey?
As a Surrey benchmark, the building work for an extension typically costs £2,500–£3,500 per m² of new floor area, before VAT. Contingency, VAT, the kitchen and bathrooms and the fees then sit on top, which is why the whole project costs more than the builder’s figure.
Is this a quote?
No. It is a range built from published benchmarks and our own recent tenders, to help you plan. Your own figure depends on the house, the site, the specification and what builders are pricing at when you tender.
What is not included?
Professional and council fees, and anything you leave as “Not yet”. They are real costs, so the true figure sits above the range until they are counted. The Clarity Pack is where they are tested against your own house.
Not sure where to start? Start here.
Fifteen minutes on the phone with James. We talk through where you are, what you are trying to achieve, and what the sensible next step looks like. There is no pressure and no obligation. Sometimes the right outcome of a call is simply a clearer head.
Book a free 15-minute Clarity Call (opens in a new tab)
No selling. Just a clear view on the smartest next step.
