Quick answer: building a typical house in the UK currently costs roughly £2,500 to £3,000 per m² for the construction alone. Add professional fees, planning, a warranty, contingency and VAT on fees, and the all-in figure for an average 120 m² home comes out nearer £3,200 per m², or about £388,000 in the Midlands. Extensions, loft conversions and renovations all have their own prices, and every one of them is in the calculator above.

Maybe you've just bought a plot. Maybe you're wondering what a kitchen extension would do to your savings, or whether a dormer loft is realistic this year. Either way you want a proper number before you start ringing builders, and a shrug and an "it depends" doesn't help anyone. That's why we built this house build cost calculator UK homeowners, self-builders and landlords can use for free. Pick the job, type in the floor area, choose your region and finish level, and it works out the construction cost, fees, contingency and VAT, then gives you a likely range and a monthly repayment.

Think of it as a UK home improvement cost calculator for the big jobs: one tool, four project types. Use it as a house construction cost calculator for a new build, as an extension cost calculator, as a renovation cost calculator, or as a loft conversion cost calculator. This guide shows you how to use every part of it, what the numbers mean, and how to sense-check any quote that lands on your doormat.

Starting rates at a glance (per m², Midlands, before fees, contingency and VAT)

How much does it cost to build a house in the UK?

Build It magazine's self-build cost guide puts a typical self-build, delivered by a main contractor to a decent specification, at £2,500 to £3,000 per m². A simple, self-managed project can come in nearer £2,200, and a high-end design with lots of bespoke detailing can pass £3,200. The calculator's Standard finish sits comfortably inside that band at £2,500 per m², with Premium at £3,150 and Luxury at £4,200.

The catch is that the per-m² rate only covers the construction bill. Take a 120 m² detached two-storey house in the Midlands at Standard finish. The build itself is £300,000. On top of that you've got an extra bathroom, architect and engineer fees at 12%, a 10% contingency, a 10-year warranty, planning and building control, and VAT on the fees. Once those are in, the calculator shows £388,042, which is £3,234 per m². That is roughly £88,000 (nearly 30%) more than you'd get from the headline rate alone, and it's the gap that catches a lot of first-time builders out.

Table 1: New build cost by house size (detached, two storeys, Standard finish, Midlands, one extra bathroom, 12% fees, 10% contingency, warranty, planning and building control, no land)

Notice that the all-in cost per m² drifts down as the house gets bigger, from £3,283 at 80 m² to £3,194 at 200 m². Fixed items like planning fees and the bathroom allowance get spread over more floor area. The drop is small, though. Don't expect a big bulk discount for building a bigger house.

That chart is worth a long look. Same size, same plot, same region, and the total swings from £308,413 to £658,906 purely on specification. If a budget feels tight, finish level is the first thing to examine, well before you start shaving square metres off the plans.

Building cost per square metre in the UK, and per square foot

Builders, quantity surveyors and mortgage valuers all think in cost per m² of floor area, because it strips out the size of the house and lets you compare projects fairly. Plenty of people still think in square feet, so the calculator has an m² / ft² switch beside every area box. If you're searching for the cost per square foot to build a house in the UK, divide any per-m² figure by 10.76. At Standard finish that works out at about £232 per ft² for a new build.

Table 2: The calculator's base rates (Midlands, before regional multiplier, fees, contingency and VAT)

The base rate is only the starting point. The calculator then nudges it up or down for the things that genuinely change the price of a build, and each one is a separate choice you can see and control.

Table 3: Multipliers applied on top of the base rate

How to use this house build and renovation cost calculator

This is the part most people skip, and it's usually why they end up with a number that looks odd. It takes about two minutes. Work down the steps below and every box on the screen will make sense, whether you're using it as a house construction cost calculator for a brand-new home or to price an extension, renovation or loft.

Field guide: new build

Field guide: extension

Field guide: renovation

Field guide: loft conversion

Table 4: Kitchen and bathroom allowances (Midlands, multiplied by your region). Renovation uses the first three rows for its three scopes.

Worked example: a 120 m² new build, line by line

Here is exactly how the default new build total is put together, so you can see there is no black box.

Table 5: Default new build, line by line

What the "likely range" means

Under the total you'll see a range, for example £349,200 to £446,200 on the build above. It's the total (without land) minus 10% at the low end and plus 15% at the high end, rounded to the nearest £100. The range leans upward on purpose, because building bills tend to drift up more often than they drift down. Treat the total as the middle of your planning budget and the top of the range as the figure you'd want to be able to survive.

Extension cost calculator: what a UK extension really costs

An extension is the job most households tackle first, and it's also the one where the headline rate misleads people most. Industry guides, including figures attributed to the Federation of Master Builders, put a single-storey extension at roughly £1,800 to £3,000 per m² nationally, with London and the South East often 20 to 40% higher. The extension tab starts from the same ground: £1,800 for a budget job, £2,400 standard, £3,000 premium and £3,800 luxury per m² in the Midlands.

Then the rest of the project piles on. A standard 20 m² single-storey extension has a build price of £48,000. Add 12% for design fees, 10% contingency, a planning fee and building control, then 20% VAT on the work, and the calculator lands on £71,520, or £3,576 per m² all-in. Unlike a new build, an extension carries the full 20% VAT, and that is the main reason the all-in number sits so far above the rate you'll hear quoted.

Table 6: Cost to extend a house, calculator results by size (single storey, Standard finish, Midlands, 12% fees, planning, building control, 10% contingency, VAT)

In the calculator the all-in rate eases from £3,638 at 10 m² to £3,545 at 40 m², because the planning and building control fees are spread over more floor area. The saving is small, so don't plan on a bargain for going bigger.

A double-storey extension is cheaper per m² (we apply ×0.85) because one set of foundations and one roof serve two floors. A wraparound costs more (×1.15) thanks to the awkward junctions where new walls meet the old house. A basement is the expensive outlier at ×1.60. One guide we checked suggests basements can run 50 to 100% above the cost of space above ground, depending on ground conditions and access.

Cost to extend a house: three things to check before you rely on any calculator

• Planning. Many single-storey rear extensions are permitted development, but conservation areas, flats and homes that have already been extended can change that. If you do need permission, the current householder fee in England is £548. That's the figure the calculator uses when "Planning permission" is ticked.
• Building control. You need building regulations approval whether or not you need planning permission, and the council's charge is usually based on size or estimated cost.
• Party walls. Building on or near a shared boundary usually means serving notice on your neighbour. The Party wall pill adds a £1,200 allowance for surveyor fees.

Loft conversion cost calculator: prices by conversion type

A loft conversion is usually the cheapest way to add a proper bedroom, because the walls, floor and roof already exist. Most current price guides put UK loft conversions somewhere between roughly £1,200 and £2,800 per m², and the type of conversion explains most of that spread. The loft conversion cost calculator on the Loft tab uses £1,700 (rooflight), £2,000 (rear dormer), £2,300 (hip-to-gable) and £2,700 (mansard) per m² at Standard finish in the Midlands, then multiplies by 1.20 for Premium and 1.45 for Luxury.

Table 7: Loft conversion cost by type (28 m² of new floor space, Standard finish, Midlands, 12% fees, building control, 10% contingency, VAT)

• Rooflight (Velux): windows set into the existing roof slope with no change to the roof shape. Quickest and cheapest, but you need decent headroom already. Around 2.2 m at the highest point is the usual starting point.
• Rear dormer: a box built out from the back slope that adds headroom and floor space. It's the most common conversion in the UK, and the one most semis and terraces end up with.
• Hip-to-gable: for houses with a sloping side roof. The slope is built up into a vertical wall to gain internal volume, and it's often paired with a rear dormer.
• Mansard: the roof is reshaped into a near-vertical rear slope with a flat top. It gives the most space, costs the most, and usually needs planning permission.

Rooflight conversions and many dormers can be permitted development, provided you stay inside the volume limits (40 m³ of extra roof space for terraced houses, 50 m³ for semis and detached). Mansards and anything that changes the front roof slope normally need planning permission, and flats and some designated areas have tighter rules, so check with your council first. An en-suite adds £9,000 in the Midlands (£12,780 in Inner London), and semis and terraces almost always need a party wall notice because the new steelwork bears on the shared wall.

Table 8: Rear dormer by size (Standard finish, Midlands)

See how flat the per-m² figure stays, at about £2,950? A loft has far fewer fixed costs than an extension, so the price follows the floor area closely.

Renovation cost calculator: light refresh, full renovation or structural

Renovation is the hardest job to price, because you never quite know what's behind the plaster. The renovation cost calculator copes by offering three scopes and a higher default contingency of 15%.

• Light refresh (£700 per m²): decorating, new flooring, minor repairs and cosmetic work, with no major services or structural changes.
• Full renovation (£1,400 per m²): the whole-house treatment: rewiring, replumbing, new heating, replastering and fresh finishes throughout.
• Structural work (£2,200 per m²): walls removed or moved, steel beams, new openings and layout changes, the kind of project that needs an engineer and building control sign-off.

Table 9: Renovation cost for a 90 m² house (Midlands, one new kitchen and bathroom, 12% fees, building control, 15% contingency, VAT at 20%)

The 5% VAT rule for empty homes

If a house has not been lived in for two years or more before the work starts, HMRC lets builders charge the reduced rate of 5% VAT on the renovation work. Tick Empty 2+ years and the calculator applies it. On the full renovation above, that takes the total from £226,102 to £200,572, a saving of £25,530. Professional fees stay at 20%, and HMRC excludes a few items (scaffolding, carpets and fitted furniture, for instance) from the reduced rate, so your real saving may be slightly smaller. Keep proof of the empty period, such as council tax records, the electoral roll or a letter from the council's empty homes officer.

Self build cost calculator: the costs people forget

When people search for a self build cost calculator, what they really want is the whole figure, not just the bricks and mortar. The New build tab is built for that. These are the items that most often go missing from a first budget, and whether the calculator handles them:

Table 10: Often-forgotten self-build costs

Build costs by region across the UK

Labour typically makes up somewhere around 40 to 50% of a build bill, and labour rates swing a lot around the country. That's why the identical house costs very different amounts depending on where you build it. The calculator uses ten regions, with the Midlands as the baseline. For the same 120 m² house, the gap between Inner London and Northern Ireland is £220,153.

Table 11: Regional build costs (Standard finish; the 120 m² figures use the default new build settings)

Two honest caveats. Regional multipliers are averages, so a builder in a pricey town in the North can still out-charge the table. And for Scotland, Wales and Northern Ireland the build rates are adjusted, but the statutory fees in the calculator follow the England schedule, so check your local planning and building control charges for those lines.

VAT on building work: what the calculator assumes

VAT is where plenty of online calculators quietly go wrong. Charge 20% on everything and you overstate a new build. Ignore VAT altogether and you understate an extension by a fifth. This calculator follows HMRC's own published VAT guidance for the building and construction industry (VAT Notice 708).

Table 12: How VAT is treated, by item

If you're building your own home, there's a second piece to the puzzle. HMRC runs a VAT refund scheme for self-builders that lets you claim back VAT paid on building materials for a qualifying new home, normally within three months of completion. The calculator doesn't subtract any refund, so your real cost could be lower than the figure shown. One warning from HMRC's own guidance: the scheme only refunds VAT that was correctly charged. If a builder bills you 20% for constructing a brand-new house, ask them to explain before you pay.

Planning, building control and party wall fees

These are the small lines that people forget until the invoices start arriving. Planning fees are set nationally. Building control and party wall costs are not, so treat the calculator's figures as typical rather than exact.

Table 13: Statutory and professional fees

Scotland, Wales and Northern Ireland have their own planning and building regulation systems, so always check the local rules before you talk to your neighbours or submit an application.

Where the money goes on a typical new build

Chart 5: the default 120 m² new build, split by cost. Construction is about 77% of the bill. The other 23% is where budgets quietly break: fees, contingency and VAT on fees alone add up to nearly a fifth (19%) of the total, and none of them show up in a headline per-m² rate. The calculator's Breakdown tab draws exactly this picture for your own project.

How long will the work take?

The calculator also gives a typical build time. These are on-site durations from the day the builders start, so add time before that for design, planning and building control approval, which can easily take several months.

Table 14: Typical build times used by the calculator

Monthly cost of a loan or mortgage

Open the Monthly cost tab and the calculator turns your total into a repayment. Using the standard repayment formula, a 25-year loan on the default new build with a 20% deposit at 5.5% costs £1,906.33 a month. You'd borrow £310,434, repay £571,900 in all, and pay £261,467 of that in interest.

Table 15: Monthly repayment on the default £388,042 new build over 25 years

Two practical points. First, 5.5% is just the starting figure on the calculator. Mortgage and loan rates move, so type in the rate you've actually been quoted. Second, self-build mortgages work differently to a normal home loan: lenders usually release the money in stages as the build progresses, and many allow interest-only payments while you're building, so early monthly costs are often lower than the table suggests. For extensions, lofts and renovations the default is 6.5% over 10 years, which suits a typical home improvement loan or further advance. If you want to compare deals, try our UK mortgage calculator suite.

Ten ways to keep your budget under control

1. Start with finish level. Run the same project at Budget, Standard and Premium. The gap is usually bigger than any other decision you'll make.
2. Keep the shape simple. Terraced and semi-detached houses cost less per m² than detached, and a plain rectangle beats a complicated footprint.
3. Don't trim the contingency to make the number look nicer. An honest 10% to 15% is what keeps a surprise from becoming a crisis.
4. Check the Extras & fees count. The little badge on the tab tells you how many extras are ticked. Make sure each tick matches reality.
5. Get the ground checked early. Switching from easy to difficult ground adds 20% to the build rate. A survey costs far less than a nasty surprise at foundation stage.
6. Sort party walls early. Notices have a time limit and disagreements add fees, so serve them well before your start date.
7. Ask how VAT will be handled. For a new build, the construction price shouldn't include 20% VAT.
8. Compare quotes line by line. Put a builder's quote next to the Breakdown tab. Big differences usually reveal something that has been left out.
9. Use the By region tab as a reality check. If a quote is far above the figure for your region and finish, ask why.
10. Get three quotes anyway. A good building cost calculator UK homeowners can trust gets you to a sensible budget, and this house construction cost calculator is built to do exactly that. It can't replace someone looking at your drawings and your site.

What the calculator doesn't include

Where the figures come from

We checked the rates and rules in this guide against these sources:

• HMRC's published VAT guidance for the building and construction industry, for every VAT rate.
• HMRC's guidance on reclaiming VAT on a self-build home.
• The official England planning fee schedule, for the £548 and £610 fees.
• Build It magazine's self-build cost guide and other current UK cost guides, for per-m² price ranges.
• Published council building control schedules, and current party wall and structural warranty price guides, for typical fees.

Frequently asked questions

Tap a question to see the answer.

Add this tool to your website

Run a property, DIY, mortgage or home improvement site? You're welcome to put this calculator on your own page for free. Copy the code below and paste it into the HTML view of your post or page. The calculator always loads our latest version, so the rates and rules stay up to date without you doing a thing. Please leave the small credit link under it in place. If the calculator looks too short or too tall on your layout, change the height value.