Financial Planning Tool
Extension ROI Calculator
Calculate whether your extension project is worth the investment. See realistic costs, estimated value increase, and net return.
Your Property
We use this to find local cost and value data
£
Your estimate or recent valuation
Heritage properties have higher build costs
Your Project
sqm
Enter custom size or we'll use typical dimensions
Sample Results: Loft Conversion in NW3
Project Cost
£75,000 - £100,000
- • Construction: £65k-85k
- • Professional fees: £8k-12k
- • Other costs: £2k-3k
Value Increase
£130,000 - £180,000
- • +15% property value
- • 40sqm new space
- • £1,450/sqft area value
Net Gain
£55,000 - £80,000
+73% ROI
✓ Worth doing
Compare Alternative Projects
| Project Type | Est. Cost | Value Add | ROI | Verdict |
|---|---|---|---|---|
| 🔺 Loft Conversion | £88k | £155k | +76% | ⭐ Best ROI |
| ↔️ Side Return | £48k | £65k | +35% | ✓ Good value |
| 🏠 Rear Extension | £58k | £78k | +34% | ✓ Good value |
| ⬇️ Basement | £260k | £310k | +19% | △ Consider carefully |
Property Values by Area
NW3
Hampstead
Avg. value
£2.5m
Price/sqft
£1,450
N6
Highgate
Avg. value
£1.8m
Price/sqft
£1,100
N10
Muswell Hill
Avg. value
£1.2m
Price/sqft
£750
N8
Crouch End
Avg. value
£1.1m
Price/sqft
£700
NW1
Primrose Hill
Avg. value
£2.2m
Price/sqft
£1,200
Ready to Get Started?
Get a detailed feasibility report for your specific property, including heritage status, planning likelihood, and recommended approach.