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Loft conversion cost calculator · free
Loft conversion cost calculator. London prices.
Answer one question at a time and watch your home take shape. Choose one project or several. Your indicative London price arrives at the end, on screen and by email. Free, and about two minutes.
Want your own project priced trade by trade, from your description, photos and plans? That is the AI Estimator, £9.99.
01Your home
What kind of home is it?
How the calculator works
Four questions, one clear range.
- 01
Your home
Terraced, semi detached, detached or a flat, and roughly when it was built. The model draws it in its period, roof included.
- 02
The kind of loft
A rear dormer, rooflights set into the existing slope, a hip to gable on a house with a hipped roof, or a mansard, which builds a new top floor.
- 03
The size and the brief
The new loft floor in square metres, the finish level, whether you have drawings, and where planning stands.
- 04
Your estimate
An indicative London range on screen, by email and as a PDF. Add an extension, a kitchen or bathrooms and they are priced together, line by line.
What London projects cost
What a loft conversion costs in London
| The work | Typical cost, ex VAT | Read more |
|---|---|---|
| A loft conversion of any type, per m² of new loft floor | £2,550 to £3,150 per m² | How the estimate prices |
| A rear dormer loft conversion, new stair included | £68,000 to £81,000 | Loft conversion costs |
| A rear dormer adding a bedroom and shower room, about 20 m² of new floor at a high specification, plus the new stair | Around £70,000 | Loft conversion costs |
| A rear dormer adding a bedroom and en suite, about 28 m² of new floor at a standard specification, plus the new stair | Around £78,000 | Loft conversion costs |
From typical London jobs priced on our estimator in October 2026, calibrated to inner west London: Fulham, Chelsea and Wandsworth. Prime central London projects often price 8 to 25 percent above these figures, and outer London commonly 10 to 20 percent below. All figures exclude VAT and are indicative, not a quotation.
What the price includes
- The building work of the conversion, the new stair from the floor below included
- The building work to the party walls
- Fitting the windows, rooflights, sanitaryware, tiles and wood flooring
- Your choice of finish level: essential, standard or high
What it leaves out
- VAT
- Professional fees: design, structural engineering, building control and party wall surveyors
- Planning and statutory costs
- The products themselves: windows, rooflights, sanitaryware, tiles and wood flooring are priced for fitting, with the products supplied by you
Good to know
Frequently asked questions
- How accurate is a loft conversion cost calculator?
- It gives an indicative range, not a quotation. Ours uses the rate MVV publishes from typical London jobs priced on its estimator, £2,550 to £3,150 per square metre of new loft floor at a standard finish, calibrated to inner west London. Every roof is different, so the final price follows a survey and the drawings.
- How much does a loft conversion cost in London?
- Typical London rear dormer loft conversions priced on our estimator in October 2026 came to £68,000 to £81,000 ex VAT, a new stair from the floor below included. One adding about 20 m² of new floor at a high specification came to around £70,000, and one adding about 28 m² at a standard specification around £78,000.
- Does the type of loft change the price?
- The calculator prices every kind of loft at the same rate per square metre of new loft floor. What separates a rooflight conversion from a mansard is mostly the floor it creates: a mansard or a large dormer adds far more usable floor than rooflights in the existing slope.
- Does the calculator include VAT and fees?
- No. Every figure is ex VAT and leaves out professional fees, planning and statutory costs, and the party wall surveyors' fees. Our design cost calculator prices the design and approvals separately.
- Is the loft conversion cost calculator free?
- Yes. It is free, with no card and no account. You leave an email address so the range and the PDF can reach you.
- Does it work outside London?
- It is calibrated to London. Prime central London projects often price 8 to 25 percent above its figures and outer London commonly 10 to 20 percent below. Outside London the figures are likely to run high.
Read more: Loft conversion cost in London · Hip to gable loft conversions · Loft conversions in London · Extension cost calculator
Estimates are indicative ranges, exclusive of VAT, professional fees, planning and statutory costs. Every MVV project is priced individually after a site visit. The estimate is where the conversation starts, not where it ends.