Loft Conversion Value Calculator

Work out loft conversion value instantly with clear inputs, formula shown and shareable results.

About Loft Conversion Value Calculator

A loft conversion adds habitable area at the local value rate, discounted about fifteen percent because loft rooms with sloping ceilings and dormer windows are valued below main floor space. Netting total cost including planning and fees against that uplift gives the real gain, which depends heavily on the local rate per square foot.

Formulas

Value added

Added = habitable area x local rate x 0.85 loft discount

Return

Return = (value added - total cost) / total cost x 100

Worked example

With the default values below, Loft Conversion Value Calculator returns Net value gain of $160,000.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Conversion costminimum 0.01: 1,800,000
Habitable area createdminimum 0.1 ft²: 400 ft²
Local value rateminimum 0 per ft²: 6,000 per ft²
Planning and professional feesminimum 0: 80,000

Results

Net value gain: $160,000.00
Value added: $2,040,000.00
Total cost: $1,880,000.00
Return on investment: 8.51% %

Step by step

1Values used
2Value added
3Return
4Net value gain= 160,000.00
5Value added= 2,040,000.00
6Total cost= 1,880,000.00
7Return on investment= 8.51 %

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Loft Conversion Value figure worked out?

Added = habitable area x local rate x 0.85 loft discount. A loft conversion adds habitable area at the local value rate, discounted about fifteen percent because loft rooms with sloping ceilings and dormer windows are valued below main floor space.

When does a loft conversion not pay?

Where the local rate per square foot is low relative to build cost, or where the conversion removes the only storage and needs an awkward staircase that sacrifices a bedroom below.

What values do I need to enter?

This calculator takes 4 inputs: Conversion cost, Habitable area created, Local value rate, Planning and professional fees. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.