Commercial-to-Residential Conversion Calculator

A C-to-R conversion is the change of use of an existing commercial building (most commonly an office, shop, or warehouse) into residential dwellings such as flats or houses. In England the most common route is Class MA prior approval (office to C3 dwellinghouse) which is faster and lighter than full planning, but full planning is still required for many shop, restaurant, and warehouse conversions, particularly in conservation areas or under Article 4 directions.

Class MA is a Permitted Development Right introduced in 2021 that lets owners convert qualifying Class E commercial space into residential C3 use under a prior-approval process rather than full planning. The building must have been in commercial use for at least two years and vacant for three months before the application. Local planning authorities can refuse on a defined list of grounds (flooding, contamination, transport, noise, light, fire safety) but cannot refuse on principle. Outside Class MA scope, you need full planning permission.

RICS BCIS benchmarks for office-to-residential conversion sit between £1,200 and £2,500 per square metre depending on building condition, services upgrade scope, and region. Inner London costs are typically 30 to 40 per cent above the UK baseline; the North East and Wales sit 10 to 15 per cent below. The calculator above uses £1,500 per square metre as the UK baseline and applies a regional multiplier; you can override it if you have a quantity surveyor figure.

GDV ranges vary widely by location. Outside London, finished residential conversions commonly sell for £3,500 to £5,500 per square metre. Inner London comparables routinely exceed £8,000 per square metre and reach £12,000 or more in prime areas. Always anchor your number to recent sold-price comparables from Land Registry rather than asking prices, and discount for conversion-specific issues such as awkward floor plates or lack of outside space.

This calculator flags any project at 20 per cent margin on cost or higher as Feasible, 10 to 20 per cent as Marginal, and below 10 per cent as Not viable. These thresholds reflect typical UK developer hurdle rates after accounting for build-cost overruns, planning delays, and sales-market risk. Funded developments will usually need 18 to 25 per cent margin to satisfy lender stress tests. A marginal verdict does not necessarily kill the deal but suggests you need either a sharper acquisition price or a refined design.

Yes. Stamp duty is calculated using the standard residential SDLT bands as a conservative proxy because once converted the asset is residential. If you intend to hold the asset commercial during the works and pay non-residential SDLT on completion, your acquisition tax will typically be lower; consult your solicitor. The additional-property surcharge toggle adds 3 percentage points across all bands, applicable for company purchases and second-property buyers.