Cost planner for homeowners
London renovation cost calculator
A realistic range for an extension, kitchen, bathroom or whole refurbishment in London. Every line a builder should include is shown separately: the works, preliminaries, contingency, professional fees and VAT.
Estimated total including VAT
£92,000 to £123,000
£77,000 to £102,000 before VAT
| Line | Range |
|---|---|
| Building works | £55,200 to £67,200 |
| Preliminaries: site set-up, management, welfare, insurance, waste | £5,500 to £9,400 |
| Contingency | £6,100 to £7,700 |
| Architect, structural engineer, Building Control, party wall and Thames Water | £10,000 to £18,000 |
- Many single-storey rear extensions fall under permitted development. Conservation areas, flats and larger extensions need planning permission.
- Work on or near a shared wall needs Party Wall Act notices: two months before party wall work, one month before excavation.
Email me this breakdown
We email the figures above as a breakdown you can keep, with six questions worth asking any builder you get quotes from.
Ready to get it priced properly? Book a site visit with these figures
An indicative range for budgeting, not a quote. Figures exclude planning application fees, furniture and anything you buy directly. Ranges last updated September 2026. Sources and method.
How the range is built
The same lines you should see on any proper quote
If a quote you receive is missing one of these, ask where it has gone. It is usually hidden in the rates or left out until later.
- Building works
- A rate per square metre (or per bathroom) for the finish level you choose. Rates come from our own recent London tenders where we have them, and from published London cost guides where we do not.
- Preliminaries
- Site set-up, project management, welfare, insurance, protection, waste and small plant. On our recent tenders this came to between 9.5% and 14% of the job, so the planner uses 10% to 14%.
- Allowances
- Items you choose, such as kitchen units and appliances. On a real schedule these appear as provisional or prime cost sums until you pick the product.
- Contingency
- A 10% line for what cannot be seen until the work is opened up. We show it separately so you can see whether it is spent.
- Professional fees
- For extensions: architect, structural engineer, Building Control, party wall surveyors and a Thames Water build-over application where needed.
- VAT
- Building work on an existing home is normally charged at 20%. Some work qualifies for 5% or 0%. See HMRC VAT Notice 708.
Not included
Costs to budget for separately
- Planning application fees. A householder application in England is currently £548.
- Furniture, curtains, loose lighting and anything you buy directly.
- Specialist surveys, such as asbestos, drainage CCTV or measured surveys, where needed.
- Moving out or storage while the work is done.
- Work to shared parts of a building that needs the freeholder or managing agent’s involvement.
Questions
Common questions about renovation costs in London
How much does a single-storey extension cost in London?
For a 24 m² extension at a standard finish, the planner gives £92,000 to £123,000 including VAT, preliminaries, a 10% contingency and professional fees, before any new kitchen. At an architect-specified finish the same extension comes to £134,000 to £184,000. Glazing, steelwork and how much of the existing house is opened up cause most of the difference.
How much does a new kitchen cost in London?
Refitting a 16 m² kitchen at a standard finish, including units, worktops, appliances, the building work around them, contingency and VAT, comes to £19,000 to £33,000. Moving the sink, hob or walls adds to that.
How much does a bathroom renovation cost in London?
One bathroom supplied and fitted at a standard finish comes to £12,000 to £17,000 including VAT and contingency. An upgraded finish with natural stone or large-format tiles and better fittings comes to £16,000 to £26,000.
How much does it cost to refurbish a two-bedroom flat in London?
For a 75 m² flat at a standard finish, without moving walls, the planner gives £82,000 to £130,000 including VAT. Leasehold flats usually need the freeholder’s written consent before work starts.
Do I pay VAT on building work to my home?
Usually yes, at 20%. The reduced 5% rate can apply to renovating a home that has been empty for two years or more, or to work that changes the number of homes in a building. Installing certain energy-saving materials can be zero-rated. HMRC VAT Notice 708 sets out the rules.
What are preliminaries on a building quote?
Preliminaries are the costs of running the site rather than building anything: set-up, project management, welfare facilities, insurance, protection, waste removal and small plant. On our recent London tenders they came to between 9.5% and 14% of the total. If a quote has no preliminaries line, those costs are inside the other rates.
Is this a quote?
No. It is a range for budgeting. The structure, services and access of your property all move the price. After a site visit we send a priced schedule of works with every line itemised.
Sources and method
Extension and bathroom rates are set from Mount St Projects tenders priced in 2025 and 2026 and cross-checked against published London guides. Kitchen and whole-home refurbishment rates rely more on published guides. Preliminaries and contingency percentages come directly from our tenders. Figures are rounded to the nearest £100 per line and £1,000 in total. Tender prices in the UK rose 3.2% in the year to Q2 2026 (BCIS), so we review the ranges every quarter.
Next step
Turn the range into a priced schedule
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Tell us about the project
Two minutes on our enquiry form, or call us. Drawings help but are not needed.
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We visit and measure
We look at the structure, services, access and neighbours: everything that moves the price.
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You receive a priced schedule of works
Every line itemised, with provisional sums and exclusions stated, so you can compare it line by line with any other quote.
or call 020 7459 4729