House Extension vs Moving House: The Real Cost Comparison (2026)
Stamp duty, estate agent fees and removal costs vs build costs and disruption — a full worked comparison of extending versus moving to a bigger home in 2026.
The transaction cost of moving that's easy to underestimate
Moving house isn't just the price difference between the old and new property — it comes with a stack of transaction costs that apply regardless of how big the upgrade is:
| Cost | Typical amount |
|---|---|
| Estate agent fee (selling) | 1-2% + VAT of sale price |
| Stamp Duty (buying, England) | 0-12%+ banded on new purchase price |
| Conveyancing/legal fees (both transactions) | £2,000-£4,000 combined |
| Removals | £600-£2,000+ |
| Survey on new property | £400-£1,500 |
| Mortgage arrangement/exit fees | £0-£1,500 |
Stamp Duty Calculator
Calculate Stamp Duty Land Tax (SDLT) for your property purchase in England.
Open Stamp Duty calculatorOn a move from a £350,000 home to a £450,000 home in England, Stamp Duty alone on the £450,000 purchase (standard rates: 0% to £125,000, 2% to £250,000, 5% from £250,000 to £925,000) works out to roughly £10,000 — before any agent, legal or removal costs are added.
The build cost of extending
| Extension type | Typical cost |
|---|---|
| Single-storey rear extension (~20-25m²) | £30,000-£60,000 |
| Kitchen extension with bi-fold doors | £40,000-£70,000 |
| Double-storey extension | £60,000-£100,000+ |
| Loft conversion with dormer | £45,000-£70,000 |
| Basement conversion | £80,000-£150,000+ |
Costs vary hugely by region (London and the South East are typically well above these ranges) and by whether structural, planning or party wall issues arise mid-project.
Mortgage Calculator
Calculate monthly mortgage payments, total interest, and full repayment cost.
Open Mortgage calculatorThe value question: does an extension "pay for itself"?
Most valuation research suggests a well-executed extension typically recovers somewhere between 50% and 100% of its cost in added property value — meaning the homeowner is often paying, in part, for a lifestyle improvement rather than a pure investment. That's not necessarily a bad trade, but it changes the comparison with moving: a move "consumes" cost in transaction fees, while an extension "consumes" cost partly in value not fully recovered — different mechanisms, similar effect on net wealth.
When extending usually wins
- The existing location, school catchment or neighbours are hard to replace.
- The space gap is modest — one extra bedroom, a bigger kitchen-diner, a home office — rather than a fundamentally different-sized home.
- The existing mortgage rate is well below current market rates, making a full remortgage to a bigger loan unattractive.
When moving usually wins
- The space gap is large (e.g. needing two extra bedrooms, a garden, or off-street parking that can't be added).
- Planning risk is high (conservation area, listed building, restrictive neighbours) making an extension uncertain or slow.
- The household wants a completely different location — school catchment, commute, or downsizing toward retirement.
Mortgage Affordability Calculator
Find out how much you could borrow based on your income and outgoings.
Open Mortgage Affordability calculatorSources
- gov.uk: Stamp Duty Land Tax rates
- Planning Portal: Permitted development and extensions
- RICS: Home extension value guidance
Frequently asked questions
Is it cheaper to extend or move house in the UK?
It depends on the size of the move — a modest single-storey extension (£30,000-£60,000) is often cheaper than moving to a home two bedrooms bigger once Stamp Duty, agent fees, legal costs and removals are included, but a large two-storey extension can approach or exceed moving costs on a mid-priced property.
How much Stamp Duty would I pay moving to a £450,000 home from a £350,000 home?
SDLT is charged on the new purchase price, not the difference — a £450,000 purchase in England attracts £10,000 in Stamp Duty under the standard bands (0% to £125,000, 2% to £250,000, 5% above that up to £925,000), plus a 5% surcharge if it's an additional property.
Does an extension add its full cost in property value?
Rarely pound-for-pound — well-executed extensions in the right area typically add somewhere between 50% and 100% of their cost in value, meaning some of the spend is 'consumed' as living improvement rather than recovered on resale.
Try the calculators
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