Move
Total: £63,300
- SDLT (HMRC)
- £35,250
- Estate-agent fee
- £8,475
- Survey
- £1,500
- Legal (sale + purchase)
- £2,500
- Removals
- £2,000
- Chain contingency (1.5%)
- £13,575
Move or extend in Merton? 2026 cost comparison
For homeowners in Merton (London Borough of Merton). Updated 2026-06-02.
In short
In Merton, the median home is valued at £565,000. Moving up by 60% to a £905,000 property triggers approximately £35,250 in Stamp Duty Land Tax (SDLT). 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 £60,486 cheaper than extending
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 £73,450 (≈13%) to your home's value — Nationwide Building Society, October 2025.
Why this comparison matters
"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."
Frequently asked questions
- Is it cheaper to extend or move in Merton?
- At Merton's median £565,000 home moving up to £905,000, the move costs about £63,300 — including £35,250 of HMRC Stamp Duty. An 18 m² high-spec side-return extension runs roughly £123,786. Moving is cheaper here by about £60,486. Your real figure depends on extension size, specification and planning constraints.
- How much stamp duty would I pay moving up in Merton?
- On a typical Merton trade-up from £565,000 to £905,000 (a 60% step up), Stamp Duty Land Tax (SDLT) is £35,250 — an effective rate of 3.90%. 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 actually cost in Merton in 2026?
- A typical 18 m² side return extension in Merton runs £124,000 all-in at high specification. This covers build (£4,200–£5,000/m²), 15% professional fees (architect, structural engineer, party wall), 20% VAT and a 10% contingency. Loft conversions use a lower £/m² rate — about £135,000 all-in for a larger 25 m² conversion. Final cost depends on access, specification and ground conditions.
- What's not included in extension quotes? Hidden costs to budget for
- Most builder quotes show the 'build' cost — typically £4,200/m² in Merton. The full all-in cost adds: 20% VAT on the whole project, 8–15% architect fees (RIBA Stages 1–4), 1% structural engineer, party wall surveyors at £800–£2,000 per neighbour, planning fees (£103–£206), Building Control £500–£1,500, kitchen fittings £8,000–£40,000+, and a 10–15% contingency. Budget the all-in figure, not the build cost.
- Do I need planning permission for an extension in Merton?
- Many single-storey rear extensions in Merton fall under Permitted Development — no planning permission needed. But those rights can be withdrawn by Article 4 directions and conservation areas in Merton, including Wimbledon Village, Wimbledon Hill Park, South Wimbledon. If your home sits in one of those, or is listed, you'll need full planning. Side extensions, large rear extensions and most wraparounds need full planning regardless. Check the London Borough of Merton planning portal first. Open the London Borough of Merton planning portal
- How long does an extension or loft conversion take in Merton?
- A typical Merton side return extension takes 12–16 weeks on site once works start, plus 8–10 weeks for London Borough of Merton to determine a full planning application. Loft conversions run 10–14 weeks on site. Add lead time for design, party wall agreements with neighbours, and contractor scheduling. Plan 4–6 months from first call to break ground, longer in conservation areas.
- Will an extension add value to my Merton 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 Merton median of £565,000, that's roughly £73,500 to £135,600 of capital uplift. Final return depends on the local market, the type of buyer in Merton, and your extension's specification.
- Can I live in my home during the extension build?
- Most Merton families stay in their home during a single-storey rear or side return extension — the build is contained to the back, and your kitchen is typically rebuilt in 2–3 weeks of disruption. Loft conversions and full wraparounds are harder: expect 4–6 weeks where one floor is unusable. Plan for temporary kitchen arrangements, school-run logistics during noisy weeks, and dust everywhere.
Compare nearby London boroughs
Nearby by median property value — useful if you're weighing a move to an adjacent price tier.
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.