Cost Calculators for London Homes
Last reviewed: 6 November 2026
Three budgeting calculators for the projects we design and build in London: extensions, loft conversions and garage conversions. Each one applies the per-square-metre rates published in our own cost guides, adds the London allowance those guides describe, and gives an indicative range in seconds. None of them is a quote, and none of them promises a price.
Extension cost calculator
Single-storey rear, side return, two-storey, wrap-around, kitchen, loft, garage, conservatory and orangery extensions.
£47,000 – £84,000
20 m² single-storey rear extension, London, before VAT
Open the calculator →Workings: the extension cost guide
Loft conversion cost calculator
Indicative London loft budget by total floor area, with the published premium-finish allowance.
£58,500 – £90,000
30 m² loft conversion, London, including VAT at 20%
Open the calculator →Workings: the loft conversion cost guide
Garage conversion cost calculator
Shell-only, standard and high-end garage conversions, scaled to the floor area you want to convert.
£24,000 – £35,000
Standard single garage conversion, London & South East, including VAT at 20%
Open the calculator →Workings: the garage conversion cost guide
Want a number for your own property?
Book a free survey and we will confirm the scope, the approvals and an indicative cost for your address.
Book a free survey →How to read these ranges
- Every rate is ours, and published. Each calculator cites the guide and the table its figures come from, and each page shows the arithmetic.
- Watch the VAT basis. Extension figures are before VAT, professional fees and contingency — that is how our extension cost guide states its rates. Loft and garage figures include VAT at 20%, because that is how those guides state theirs. Every calculator labels its own basis.
- London is already included. The calculators apply the London allowance our guides publish, so the range you see is a London range, not a national one.
- These are budgets, not prices. Access, condition, ground conditions, party walls, specification and timing all move a real quote. That is what the free survey is for.
What you can do next
Read the workings in the UK cost guides — start with house extension costs, loft conversion costs and garage conversion costs — or book a free survey and we will price your property properly.