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 contingency (1.5%)
- £20,400
City of London: is it cheaper to extend or move in 2026?
For homeowners in City of London (City of London Corporation). Updated 2026-06-11.
Square Mile financial district. Residential stock dominated by Barbican flats, office-conversion apartments and a small inventory of pre-1939 buildings. Householder extensions are not a meaningful local market.
The borough covers the EC1A, EC1M, EC1N, EC1R, EC1V, EC1Y, EC2A, EC2M, EC2N, EC2R, EC2V, EC2Y, EC3A, EC3M, EC3N, EC3R, EC3V, EC4A, EC4M, EC4N, EC4R, EC4V, EC4Y postcode districts.
In short
In City of London, the average home is valued at £850,000. Moving up by 60% to a £1,360,000 property triggers approximately £79,750 in Stamp Duty Land Tax (SDLT). By contrast, a 22 m² high-spec rear extension (single storey) here costs around £108,537 all-in. The average home here is around £850,000 (ONS, 2026).
Your numbers
Adjust the inputs to see your scenario. The page updates instantly as you adjust the inputs.
Your result
Extending saves you £10,363
Extend
Rear extension (single storey) — high spec
Total: £108,537
- Build cost (22 m² × £3,300/m²)
- £72,600
- Professional fees (15%)
- £10,890
- Subtotal
- £83,490
- VAT (20%)
- £16,698
- Contingency (10%)
- £8,349
An extension of this type and size could add roughly £110,500 (≈13%) to your home's value — Nationwide Building Society, October 2025.
Your tipping line
Where moving starts costing more than the extension you selected. The chart follows your inputs above.
Up to about £1,270,000 of target price, moving is the cheaper route in City of London; beyond that line, extending wins.
Extending in City of London: what's different here
Local planning picture
- Conservation areas
- 28
- Householder decisions within 8 weeks
- 50%
- Build-cost tier
- outer London
- Typical housing stock
- 1930s semi-detached homes
Decision speed: MHCLG householder statistics, year ending September 2025, excluding agreed extensions of time.
Worth knowing in City of London
- The average home here is around £850,000 (ONS, 2026).
- Extension types suited to 1930s semi-detached homes: Rear extension (single storey), Rear extension (double storey), Two-storey side extension, Garage conversion, Loft conversion (hip-to-gable), Over-garage extension.
How the £79,750 stamp duty stacks up
HMRC bands applied to a £1,360,000 purchase — the default City of London trade-up.
| Price band | Rate | SDLT due |
|---|---|---|
| £0 – £125,000 | 0% | £0 |
| £125,000 – £250,000 | 2% | £2,500 |
| £250,000 – £925,000 | 5% | £33,750 |
| £925,000 – £1,500,000 | 10% | £43,500 |
What each suitable type costs vs the £118,900 move
High specification at typical size, outer London rates, all-in.
| Extension type | All-in cost | vs moving |
|---|---|---|
| Rear extension (single storey) (22 m²) | £108,537 | saves £10,363 vs moving |
| Rear extension (double storey) (45 m²) | £208,553 | £89,653 more than moving |
| Two-storey side extension (35 m²) | £167,440 | £48,540 more than moving |
| Garage conversion (18 m²) | £43,056 | saves £75,844 vs moving |
| Loft conversion (hip-to-gable) (25 m²) | £67,275 | saves £51,625 vs moving |
| Over-garage extension (18 m²) | £34,983 | saves £83,917 vs moving |
Why this comparison matters
"An architect-designed house extension in London may cost between £3,000 and £5,000 per square metre. Elsewhere in the UK, you can expect to pay between £2,000 and £3,500 per square metre."
Frequently asked questions
- Is it cheaper to extend or move in City of London?
- At City of London's average £850,000 home moving up to £1,360,000, the move costs about £118,900 — including £79,750 of HMRC Stamp Duty. A 22 m² high-spec rear extension (single storey) runs roughly £108,537 at outer London rates. Extending is cheaper here by about £10,363. Your real figure depends on extension size, specification and planning constraints.
- How long does a rear extension (single storey) take in City of London?
- Allow around 16 weeks on site for a typical rear extension (single storey) in City of London, after design, party wall agreements with neighbours and the council's determination period. A rear extension (double storey) runs nearer 20 weeks. End to end, plan 4–8 months from first call to completion — longer in conservation areas or where structural surveys are needed.
- Will an extension add value to my City of London home?
- Nationwide Building Society (October 2025) found that adding a double bedroom can lift a home's value by about 13%, and a full loft conversion plus extension by up to 24%. On a City of London average of £850,000, that's roughly £110,500 to £204,000 of capital uplift. Final return depends on the local market, the type of buyer in City of London, and your extension's specification.
- Can I live in my home during the extension build?
- Most City of London families stay in their home during a rear extension or garage conversion — works are contained to one side of the house. Two-storey side extensions and hip-to-gable lofts are noisier: expect 4–6 weeks where one floor or the driveway side is out of action. Plan temporary kitchen arrangements and dust control for the noisy weeks.
- At what price does moving stop making sense in City of London?
- Starting from City of London's average £850,000 home with a 22 m² high-spec rear extension (single storey) (£108,537 all-in), the tipping line sits at roughly £1,270,000: buying above that price costs more in SDLT and moving fees than the extension itself. Below it, moving stays the cheaper route. The live chart on this page recalculates the line for your own inputs.
- How much stamp duty would I pay moving up in City of London?
- On a typical City of London trade-up from £850,000 to £1,360,000 (a 60% step up), Stamp Duty Land Tax (SDLT) is £79,750 — an effective rate of 5.86%. First-time buyers and additional-property buyers pay different rates. Use HMRC's official calculator at tax.service.gov.uk for your exact figure. HMRC Stamp Duty calculator
- What does a typical extension cost in City of London in 2026?
- A 22 m² rear extension (single storey) in City of London runs about £109,000 all-in at high specification, on outer London build rates of around £3,300/m². A 45 m² rear extension (double storey) comes to roughly £209,000. All-in figures include 15% professional fees, 20% VAT and a 10% contingency — final cost depends on access, specification and ground conditions.
- How long does planning permission take in City of London?
- The statutory determination period for a householder application is 8 weeks. City of London Corporation decided 50% of householder applications within 8 weeks in the year to September 2025 (MHCLG figures, excluding agreed extensions of time) — among the slowest in London. Across London, authorities grant roughly low-to-mid 80s per cent of applications. A householder application costs £548 from April 2026, and a Larger Home Extension prior approval £240.
- Do I need planning permission for an extension in City of London?
- Many single-storey rear extensions fall under Permitted Development — no planning permission needed. The City of London Corporation operates city-wide Article 4 directions affecting office-to-residential conversions and façade alterations to historic buildings. Householder extensions are largely irrelevant in the Square Mile as residential stock is dominated by flats and commercial conversions; nearly all proposed works on the limited residential stock require full planning permission regardless of PD class. City of London has 28 conservation areas, including Bank, Barbican and Golden Lane, Blackfriars, where PD rights are curtailed. Side extensions, large rear extensions and most wraparounds need full planning regardless. Check the City of London Corporation planning portal first. Open the City of London Corporation planning portal
Compare nearby London boroughs
Nearby by average property value — useful if you're weighing a move to an adjacent price tier. A comparable trade-up in Westminster would carry about £78,750 of stamp duty — £1,000 less than in City of London.
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. Extension costs use outer London £/m² rates by extension type — industry-estimate midpoints, presented as approximations.
- MHCLG planning statistics (PS2 dashboard) — householder decision speed, year ending September 2025.
- London 2026 £/m² grid by extension type and tier — Build Team benchmark compiled from BCIS/RICS, FMB and published architect guides (refreshed quarterly).
- Conservation-area counts and Article 4 status — individual London borough councils, verified 2026.
- 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 / ONS UK House Price Index — borough average property values (March 2026 release).