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Move or extend in London? 2026 cost comparison calculator

Live calculator across all 33 London boroughs. Updated 2026-06-02.

In short

A 2026 UK calculator comparing the cost of moving house in London — Stamp Duty Land Tax (SDLT), agent fees, conveyancing, surveys, removals and chain contingency — against the cost of extending your existing home. Above about £900,000, SDLT alone on a like-for-like trade-up often rivals a well-specified extension. Nationwide Building Society's October 2025 House Price Index found that adding a double bedroom can lift home value by about 13%, and a full loft plus extension by up to 24%.

Your numbers

Adjust the inputs to see your scenario. The page updates instantly as you adjust the inputs.

Property values

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Our tool assumes your new property costs more than your current one.

Extension type
Spec tier
18 m²
Advanced: buyer profile

Know your borough? Pick it below for local prices, council planning portal links and Article 4 status.

Your result

Moving is £26,379 cheaper than extending

Move

Total: £77,225

SDLT (HMRC)
£46,250
Estate-agent fee
£9,600
Survey
£1,500
Legal (sale + purchase)
£2,500
Removals
£2,000
Chain contingency (1.5%)
£15,375

Extend

Total: £103,604

Build cost (18 m² × £3,850/m²)
£69,300
Professional fees (15%)
£10,395
Subtotal
£79,695
VAT (20%)
£15,939
Contingency (10%)
£7,970

An extension of this type and size could add roughly £83,200 (≈13%) to your home's value — Nationwide Building Society, October 2025.

Find your borough

All 33 London boroughs covered. Each borough page has local median prices, local council planning portal links, conservation-area notes and a live calculator.

How the comparison works

The move total combines HMRC Stamp Duty Land Tax on the new property with the typical UK transaction friction: a 1.5% estate-agent fee on the sale, a £1,500 survey, £2,500 of combined sale and purchase legal fees, £2,000 removals and a 1.5% chain contingency on the trade-up.

The extend total uses 2026 London £/m² ranges by extension type and specification tier, grossed up with 15% professional fees, 20% VAT and a 10% contingency on (build + fees).

The calculator's headline is out-of-pocket cost. The capital uplift from an extension is a separate consideration:

"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 London in 2026?
At London's median family-home value of around £640,000, moving up by 60% to £1,025,000 costs roughly £77,225 all-in — driven mainly by £46,250 of HMRC Stamp Duty. A typical 18 m² mid-spec side-return extension runs about £103,604 in 2026. For most homes above £900,000, extending undercuts a like-for-like trade-up.
How much is stamp duty when moving to a more expensive London home?
Stamp Duty Land Tax scales steeply above £925,000 (10%) and £1.5 million (12%) for a main residence. Moving from a £900,000 home to a £1,440,000 one triggers about £67,000 of SDLT — significantly more if you'll still own another property or are a non-UK resident. Verify any figure against HMRC's calculator at tax.service.gov.uk.
How much does a house extension cost in London?
London 2026 mid-tier ranges run roughly £2,500–£3,250 per square metre for loft and kitchen extensions, and £3,500–£4,200 for side returns. Add 15% professional fees, 20% VAT and 10% contingency on top of the build cost. A typical 18–25 m² project lands between £85,000 and £135,000 all-in at mid specification.
Does an extension add value to a 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 a £640,000 London family home that is roughly £83,200 to £153,600 of capital uplift — actual figures depend on the local market and specification.
Do I need planning permission to extend in London?
Some extensions qualify for permitted development (PD) under the GPDO 2015, but London boroughs frequently impose Article 4 directions that withdraw PD rights in specific zones — especially conservation areas. Always check the planning portal of your borough council and the Article 4 status for your address before relying on PD for any extension.
How do I find the rules for my specific borough?
Use the borough index below — every London borough has a dedicated page with local median prices, council planning portal links, conservation-area lists and Article 4 status. The calculator updates live as you adjust the inputs, so you can model your own scenario with borough-specific defaults rather than the London-wide figures shown here.
Sources and methodology references
  • HMRC SDLT calculator — tax.service.gov.uk/calculate-stamp-duty-land-tax
  • Nationwide House Price Index, October 2025 — Andrew Harvey commentary.
  • HM Land Registry UK House Price Index — borough medians, March 2026 release.
  • London 2026 £/m² grid — internal Build Team benchmark (BCIS TPI reference).
  • TwentyCi Q1 2026 — chain fall-through and abortive-cost figures.