Is it cheaper to extend or move in City of London?

At City of London's median £850,000 home moving up to £1,360,000, the move costs about £118,900 — including £79,750 of HMRC Stamp Duty. An 18 m² high-spec side-return extension runs roughly £123,786. Moving is cheaper here by about £4,886. Your real figure depends on extension size, specification and planning constraints.

How much SDLT would I pay moving up in City of London?

On City of London's median £850,000 home moving up to £1,360,000 (a 60% trade-up), HMRC Stamp Duty works out at £79,750 for a main residence — an effective rate of 5.86%. Use HMRC's calculator at tax.service.gov.uk for your exact figure if you're a first-time buyer or will still own another property.

How much does a side return extension cost in City of London in 2026?

London 2026 high-tier side-return rates run £4,200–£5,000 per square metre (midpoint £4,600). A typical 18 m² extension grosses up to about £123,786 all-in: build, 15% professional fees, 20% VAT and 10% contingency. The figure excludes finishes that go beyond the specification tier you select in the calculator.

Does City of London have planning restrictions for extensions?

Yes — local rules apply. City of London Corporation administers planning in City of London. Article 4 directions can withdraw permitted-development rights in specific areas. Notable conservation areas include Bank, Barbican and Golden Lane, Blackfriars. Check the City of London Corporation planning portal before relying on PD rights for any householder extension.

How long does a loft conversion take in City of London?

A loft conversion typically takes 10–14 weeks on site once works start, plus 8–10 weeks for City of London Corporation to determine a full planning application — or roughly 8 weeks under the prior-approval larger-extension route. Add lead time for design, party-wall agreements and contractor scheduling. Plan early if your home falls in a conservation area or under Article 4.

What value does an extension add to a City of London home?

Nationwide Building Society reported in October 2025 that adding a double bedroom can lift a home's value by about 13%, and a full loft plus extension by up to 24%. On City of London's median £850,000 that is roughly £110,500 to £204,000 of capital uplift — final figures depend on the local market and your specification.

What's the chain fall-through risk if I sell my City of London home?

TwentyCi reported a 23.7% UK property-chain fall-through rate in the first quarter of 2026, with typical abortive costs of about £2,500 in legal, survey and search fees per failed attempt. In City of London's competitive market, the risk is real. Staying put and extending avoids the chain entirely — a factor the headline calculator does not directly price in.

Do I need an architect for an extension in City of London?

For most extensions, yes. RIBA Stages 1–4 (concept through technical design) typically run 8–15% of the build cost. Strictly permitted-development side extensions or modest rear projections may not require one, but City of London's conservation areas and any Article 4 directions usually demand designed drawings to secure planning. Budget for the fee.

Move or extend in City of London? 2026 cost comparison

For homeowners in City of London (City of London Corporation). Updated 2026-05-27.

TL;DR

In City of London, the median home is valued at £850,000. Moving up by 60% to a £1,360,000 property triggers approximately £79,750 in HMRC Stamp Duty Land Tax. By contrast, an 18 m² high-spec side-return extension costs around £123,786 all-in. The Nationwide Building Society reported in October 2025 that such an extension can add 13–24% to a three-bedroom home's value.

Your numbers

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Your result

Moving is £4,886 cheaper than extending

Move

Total: £118,900

SDLT (HMRC): £79,750
Estate-agent fee: £12,750
Survey: £1,500
Legal (sale + purchase): £2,500
Removals: £2,000
Chain buffer (1.5%): £20,400

Extend

Total: £123,786

Build cost (18 m² × £4,600/m²): £82,800
Professional fees (15%): £12,420
Subtotal: £95,220
VAT (20%): £19,044
Contingency (10%): £9,522

An extension of this type and size could add roughly £110,500 (≈13%) to your home's value — Nationwide Building Society, October 2025.

"Homeowners that add a loft conversion or extension, incorporating a large double bedroom and bathroom, can add as much as 24% to the value of a three-bedroom, one-bathroom house."

— Andrew Harvey, Senior Economist, Nationwide Building Society, October 2025

Frequently asked questions

Is it cheaper to extend or move in City of London?: At City of London's median £850,000 home moving up to £1,360,000, the move costs about £118,900 — including £79,750 of HMRC Stamp Duty. An 18 m² high-spec side-return extension runs roughly £123,786. Moving is cheaper here by about £4,886. Your real figure depends on extension size, specification and planning constraints.
How much SDLT would I pay moving up in City of London?: On City of London's median £850,000 home moving up to £1,360,000 (a 60% trade-up), HMRC Stamp Duty works out at £79,750 for a main residence — an effective rate of 5.86%. Use HMRC's calculator at tax.service.gov.uk for your exact figure if you're a first-time buyer or will still own another property.
How much does a side return extension cost in City of London in 2026?: London 2026 high-tier side-return rates run £4,200–£5,000 per square metre (midpoint £4,600). A typical 18 m² extension grosses up to about £123,786 all-in: build, 15% professional fees, 20% VAT and 10% contingency. The figure excludes finishes that go beyond the specification tier you select in the calculator.
Does City of London have planning restrictions for extensions?: Yes — local rules apply. City of London Corporation administers planning in City of London. Article 4 directions can withdraw permitted-development rights in specific areas. Notable conservation areas include Bank, Barbican and Golden Lane, Blackfriars. Check the City of London Corporation planning portal before relying on PD rights for any householder extension.
How long does a loft conversion take in City of London?: A loft conversion typically takes 10–14 weeks on site once works start, plus 8–10 weeks for City of London Corporation to determine a full planning application — or roughly 8 weeks under the prior-approval larger-extension route. Add lead time for design, party-wall agreements and contractor scheduling. Plan early if your home falls in a conservation area or under Article 4.
What value does an extension add to a City of London home?: Nationwide Building Society reported in October 2025 that adding a double bedroom can lift a home's value by about 13%, and a full loft plus extension by up to 24%. On City of London's median £850,000 that is roughly £110,500 to £204,000 of capital uplift — final figures depend on the local market and your specification.
What's the chain fall-through risk if I sell my City of London home?: TwentyCi reported a 23.7% UK property-chain fall-through rate in the first quarter of 2026, with typical abortive costs of about £2,500 in legal, survey and search fees per failed attempt. In City of London's competitive market, the risk is real. Staying put and extending avoids the chain entirely — a factor the headline calculator does not directly price in.
Do I need an architect for an extension in City of London?: For most extensions, yes. RIBA Stages 1–4 (concept through technical design) typically run 8–15% of the build cost. Strictly permitted-development side extensions or modest rear projections may not require one, but City of London's conservation areas and any Article 4 directions usually demand designed drawings to secure planning. Budget for the fee.

Methodology and sources

Stamp Duty Land Tax is calculated from the HMRC bands in force for the 2025–26 tax year. Verify any figure against HMRC's official calculator before committing.

HMRC SDLT calculator — tax.service.gov.uk/calculate-stamp-duty-land-tax
GOV.UK Stamp Duty Land Tax guidance — gov.uk/stamp-duty-land-tax
Nationwide House Price Index (October 2025 release) — value-add commentary attributed to Andrew Harvey, Senior Economist.
HM Land Registry UK House Price Index — borough median property values (March 2026 release).
London 2026 £/m² grid — internal Build Team benchmark (BCIS Tender Price Index reference, refreshed quarterly).
TwentyCi market data, Q1 2026 — chain fall-through and abortive-cost figures.