Extend or Move? The Real Cost Comparison
Should you extend or move to a bigger home? A financial comparison of the true costs of moving vs extending, including stamp duty and fees.
It's one of the biggest decisions a UK homeowner faces: do you extend the home you have, or sell up and buy somewhere bigger? The emotional pull often points towards a fresh start, but the financial case almost always favours extending. Here's the full breakdown to help you decide.
The True Cost of Moving
Moving house involves a long list of fees that many homeowners underestimate. Here's what it actually costs to sell a £300,000 home and buy at £400,000:
| Fee | Typical Cost |
|---|---|
| Estate agent (1.5% of sale price) | £4,500 |
| Solicitor / conveyancer (sale + purchase) | £2,000–£3,500 |
| Stamp duty (on £400,000 purchase) | £7,500 |
| Survey (RICS Level 2 or 3) | £500–£1,500 |
| Mortgage arrangement fee | £500–£1,500 |
| Removal company | £1,000–£2,500 |
| EPC certificate | £60–£120 |
| Repairs, cleaning, and decoration (new home) | £1,000–£5,000 |
| Redirected mail, new curtains, and incidentals | £500–£1,500 |
| Total | £17,500–£27,000 |
And that's before the higher mortgage payments. If you're moving from a £300,000 home to a £400,000 home, you're adding £100,000 to your mortgage. At 4.5% over 25 years, that's an extra £555 per month - or £166,500 in total repayments.
Stamp Duty at Different Price Points
| Purchase Price | Stamp Duty | Notes |
|---|---|---|
| £250,000 | £0 | Nil-rate band |
| £300,000 | £2,500 | 5% on £50k above threshold |
| £400,000 | £7,500 | |
| £500,000 | £12,500 | |
| £600,000 | £17,500 | |
| £750,000 | £25,000 | |
| £1,000,000 | £41,250 | 10% band kicks in at £925k |
Stamp duty is a pure sunk cost - you get nothing tangible in return. That £7,500–£25,000 could fund a significant portion of an extension instead.
The True Cost of Extending
An extension's cost depends on the type, size, and your location. Here's the all-in cost including professional fees, Building Control, and making good:
| Extension Type | Typical All-In Cost | Space Added |
|---|---|---|
| Garage conversion | £12,000–£22,000 | 15–18m² |
| Loft conversion (dormer) | £38,000–£60,000 | 20–30m² |
| Single-storey rear (20m²) | £40,000–£65,000 | 20m² |
| Kitchen extension (25m²) | £50,000–£85,000 | 25m² |
| Double-storey rear (20m² footprint) | £60,000–£100,000 | 40m² |
Use our free quote calculator for a personalised estimate based on your location and specification.
The Financial Comparison
Let's compare a real scenario. A family in a 3-bed semi worth £300,000 needs more space - either a 4th bedroom and larger kitchen.
Option A: Move to a 4-Bed
| Item | Cost |
|---|---|
| Purchase price of 4-bed | £400,000 |
| Minus sale of current home | −£300,000 |
| Net price difference | £100,000 |
| Estate agent fees | £4,500 |
| Solicitor (both transactions) | £3,000 |
| Stamp duty | £7,500 |
| Survey + mortgage fees | £1,500 |
| Removals | £1,500 |
| Decoration and repairs (new home) | £3,000 |
| Total cost to move | £121,000 |
Option B: Extend
| Item | Cost |
|---|---|
| Loft conversion (new bedroom + en-suite) | £45,000 |
| Kitchen extension (20m² open-plan) | £55,000 |
| Hidden costs + contingency | £12,000 |
| Total cost to extend | £112,000 |
| Estimated value added to property | £60,000–£90,000 |
| Net cost after value gain | £22,000–£52,000 |
The extension delivers equivalent space for a similar upfront cost - but you also gain £60,000–£90,000 in property value. Moving creates zero equity; the fees are a dead cost.
The Decision Framework
Extend When...
- You love your location - school catchment, commute, community
- Your home has room to grow - garden space, loft potential, garage to convert
- The street supports the value - comparable extended homes sell for enough to justify the investment
- You want to build equity - extensions add value; moving fees don't
- You want to avoid chain risk - no failed sales, no gazumping, no chain collapses
Move When...
- You need a different area - new job, schools, downsizing, lifestyle change
- Your plot is maxed out - tiny garden, no loft potential, already extended
- The ceiling price limits returns - if every house on the street sells for £280k–£320k, a £100k extension won't take yours to £420k
- The home has fundamental problems - flood risk, structural issues, poor orientation, noise
- You want a bigger garden - extensions give more house, not more land
Hidden Advantages of Extending
1. No Chain
You're not relying on a chain of buyers and sellers. An extension project is entirely within your control - no gazumping, no delays waiting for someone else's mortgage offer.
2. You Keep Your Neighbourhood
Schools, GP, friends, local shops, commute route - all unchanged. The value of an established life in a community is hard to quantify but very real.
3. You Design Exactly What You Want
A new-to-you house is a compromise - someone else's layout, kitchen, and decoration. An extension is built to your specification.
4. No Stamp Duty
Every pound saved on stamp duty is a pound that could go into your build budget.
5. Staged Approach
You can extend in phases - a loft conversion now, a kitchen extension in 2–3 years - spreading the cost and disruption.
When the Numbers Are Close
If the financial comparison is tight, consider these tiebreakers:
| Factor | Favours Extending | Favours Moving |
|---|---|---|
| Disruption tolerance | Medium (stay in home during build) | High (moving is a one-off event) |
| Time to enjoy the space | 6–12 months to build | Available immediately after move |
| Financial risk | Build costs can overrun (budget 10–15% contingency) | Market risk (property could lose value) |
| Emotional attachment | Want to stay | Ready for a change |
| Family timing | School year, newborns - disruption is manageable | Gap between school years or before children |
How to Check the Ceiling Price
Before committing to a major extension, verify that your street supports the added value:
- Check recent sales on your road - use the Land Registry's Price Paid data (free)
- Look for extended comparable homes - what did a similar extended house sell for?
- Get an estate agent's opinion - ask 2–3 local agents what your home would be worth with the proposed extension
- Calculate the maximum - if the ceiling is £350k and your home is worth £300k, spending more than £50k on an extension risks overcapitalising
Next Steps
- Run the numbers - cost out both scenarios using real figures for your area
- Get an extension quote - our free calculator gives a detailed cost breakdown
- Check comparable sales - what do extended homes on your street sell for?
- Talk to a mortgage broker - compare the cost of a larger mortgage (moving) vs a smaller one (extending)
- Read about financing your extension if borrowing
- Understand which improvements add most value to prioritise the highest-ROI projects
Frequently Asked Questions
Ready to Get a Quote?
Use our free calculator to get a personalised, itemised estimate for your project - tailored to your location and specification.