A renovation is the biggest cheque most people write after the mortgage, and it is the one they go into with the least information. The builder gives a number, the neighbour quotes a different one, and the internet says everything from a bargain to a fortune. Without a baseline, you cannot tell a fair quote from a fleecing.
This calculator gives you that baseline. Set your project type, floor area, specification and region above, and watch a realistic cost range appear in real time, with the cost per square metre and a directional split of where the money goes.
How to read the results
- Estimated cost is the headline: a low-to-high range for your spec and region, with labour and materials included. We show a range, never a single number, because that is honest about how much UK build costs move.
- Low end and high end bracket the range at plus or minus 15 percent of the central estimate. Where you land inside it depends on access, condition and how tightly the job is specified.
- Cost per m2 appears for full renovations and extensions, the figure you can compare against published build cost guides and against other quotes on a like-for-like basis.
- Labour, materials and prelims split the build cost directionally: roughly 45 percent labour, 40 percent materials, and 15 percent for prelims, skip hire and contingency. Real splits vary, but this shows you why labour-heavy jobs behave differently from materials-heavy ones.
What actually drives UK renovation cost
Four things move the number more than anything else. Size is the obvious one: per-square-metre projects scale almost linearly, so a bigger extension simply costs more. Specification is the quiet killer, because the same footprint can cost almost double between a basic and a high-end finish once you factor in bespoke joinery, premium tiling and underfloor heating. Structural work, which a calculator cannot see, is the wildcard: knocking through a load-bearing wall, underpinning, or fixing a roof you did not know was failing can add five figures in a single afternoon. And the condition of the property decides how much you spend before you have anything to show for it, because old wiring, damp and rot all have to be dealt with before the nice part begins.
Why region changes everything
A kitchen fit in central London and the same kitchen fit in the North East are not the same job on the invoice, even with identical units. Trade day rates, builder overheads and material delivery all cost more in the South East, and London sits at the top. The calculator applies a regional factor so the estimate reflects where the work happens: London at 1.3, the South East at 1.15, the Midlands as the 1.0 baseline, and the North and the rest of the UK at 0.9. If you are comparing a London quote against a national average you read somewhere, you are comparing two different things.
Reading the range, not the number
The single most useful habit when budgeting a renovation is to stop asking "what will it cost" and start asking "what is the range, and what pushes me to the top of it". This tool answers the first half. The second half is about your choices: a tight specification, good access and a property in decent condition keep you near the low end; bespoke finishes, awkward access, structural surprises and a tired old building push you to the high end and beyond. Treat the high end as the realistic figure to keep in reserve, not the worst case, because UK renovations overrun far more often than they come in under.
Before you commit
Use the estimate to brief builders and to sanity-check the quotes that come back, not as a price to hold anyone to. Get at least three itemised quotes, cross-check the cost per square metre against published build cost guides, and keep a separate contingency on top. If you are weighing up a kitchen or bathroom specifically, the kitchen and bathroom fitting cost estimator breaks those jobs down in more detail. To understand how good builders build their numbers in the first place, the guide on the science of pricing for tradespeople is worth reading, and the marketing guide for builders and renovators explains how the firms worth hiring present and win work.
If you run a building or renovation business and want your quotes to win more often without a race to the bottom on price, see how we help builders and renovators, explore the rest of the free tools, and talk to us when you are ready.