Resources · Cost Planner
How we calculate these numbers.
Every figure the Cost Planner shows is built from the tables on this page. They are published so you can check them, argue with them, or take them to a builder.
Rates version 5 · last reviewed 27 August 2026
What changed on 27 August 2026
We re-based every rate against the sources listed below, and we started showing VAT, professional fees, the statutory planning fee and a contingency as separate lines instead of leaving them out. Estimates went up noticeably — and most of that rise is those lines, not the rates. The published rates every UK cost guide quotes are the builder's work only, before VAT. A tool that showed you that number and called it your budget was understating what you actually need to find.
The calculation
- Take the trade's rate for the specification you picked, and multiply it by your size.
- Multiply by the regional multiplier for your area.
- Add professional fees — design, structural calculations and building control — which also scale by region.
- Add the statutory planning fee where planning applies. This is set by government, so it is the same everywhere and is not scaled.
- Add VAT at the applicable rate.
- Add contingency, as a percentage of everything above.
- That gives one figure. The published range is that figure multiplied by 0.82 and by 1.28.
The range is deliberately lopsided. Building work overruns far more often than it comes in under, so a symmetrical range would understate the risk that matters. Every figure is rounded to the nearest £100 inside the model and never re-rounded for display, which is why the lines on the result card add up exactly.
Specification
Specification chooses which rate you are priced at — not how wide the range is. The three tiers are three different rates per trade, and the range is a separate allowance for uncertainty around whichever one you picked.
- Essential materials
- Budget ranges, trade-standard fittings, keeping it simple. Priced at each trade's low rate below.
- Standard materials
- Mid-range brands and finishes — what most projects use. Priced at each trade's mid rate below.
- Premium materials
- High-end materials, bespoke joinery, designer fittings. Priced at each trade's high rate below.
Rates by trade
Per unit of size, excluding VAT — this is the builder's work only. Everything else is in the next table.
| Trade | Per | Essential | Standard | Premium |
|---|---|---|---|---|
| Extension | m² | £1,850 | £2,350 | £3,050 |
| Loft Conversion | m² | £1,300 | £1,850 | £2,500 |
| Renovation | m² | £600 | £900 | £1,700 |
| New Build | m² | £1,800 | £2,400 | £3,400 |
| Garden / Landscaping | m² | £55 | £110 | £180 |
| Kitchen | room | £6,000 | £11,000 | £22,000 |
| Bathroom | room | £4,000 | £7,000 | £13,000 |
| Plumbing | wet room | £1,250 | £1,700 | £2,400 |
| Electrical | m² | £48 | £68 | £95 |
| Roofing | m² | £85 | £120 | £200 |
| Windows & Doors | opening | £350 | £545 | £1,225 |
| Plastering | room | £400 | £560 | £775 |
| Painting & Decorating | m² | £40 | £50 | £80 |
| Flooring | m² | £28 | £53 | £110 |
| Driveways & Paving | m² | £55 | £105 | £170 |
| Other | m² | £550 | £1,075 | £2,100 |
What gets added on top
| Trade | Fees (standard) | Planning | Contingency | VAT |
|---|---|---|---|---|
| Extension | £6,300 | £548 | 10% | 20% |
| Loft Conversion | £3,600 | £548 | 10% | 20% |
| Renovation | £2,600 | £0 | 10% | 20% |
| New Build | £13,300 | £548 | 10% | 0% |
| Garden / Landscaping | £650 | £0 | 5% | 20% |
| Kitchen | £400 | £0 | 5% | 20% |
| Bathroom | £350 | £0 | 5% | 20% |
| Plumbing | £1,400 | £0 | 5% | 20% |
| Electrical | £280 | £0 | 5% | 20% |
| Roofing | £280 | £0 | 5% | 20% |
| Windows & Doors | £600 | £0 | 0% | 20% |
| Plastering | £300 | £0 | 0% | 20% |
| Painting & Decorating | £0 | £0 | 0% | 20% |
| Flooring | £0 | £0 | 0% | 20% |
| Driveways & Paving | £0 | £0 | 0% | 20% |
| Other | £2,500 | £0 | 5% | 20% |
Regions
The multiplier applies to the rate and to professional fees. It is a best fit by postcode area, not a boundary-accurate lookup — a few areas straddle a border and are assigned to where most of their population lives. If we have guessed wrong for you, pick the region by hand. An unrecognised postcode falls back to the UK average rather than to a guess.
| Region | Multiplier | Postcode areas |
|---|---|---|
| UK average | ×1.00 | Used when no postcode is given, or none matches |
| London (inner) | ×1.30 | EC, WC, W, SW, NW, N, E, SE |
| London (outer) | ×1.22 | BR, CR, DA, EN, HA, IG, KT, RM, SM, TW, UB, WD |
| South East | ×1.12 | BN, CT, GU, HP, ME, MK, OX, PO, RG, RH, SL, SO, TN |
| East of England | ×1.05 | AL, CB, CM, CO, IP, LU, NR, PE, SG, SS |
| South West | ×1.00 | BA, BS, DT, EX, GL, PL, SN, SP, TA, TQ, TR |
| West Midlands | ×1.00 | B, CV, DY, HR, ST, TF, WR, WS, WV |
| East Midlands | ×1.00 | DE, LE, LN, NG, NN |
| Yorkshire & the Humber | ×0.93 | BD, DN, HD, HG, HU, HX, LS, S, WF, YO |
| North West | ×0.95 | BB, BL, CH, CW, FY, L, LA, M, OL, PR, SK, WA, WN |
| North East | ×0.94 | CA, DH, DL, NE, SR, TS |
| Wales | ×0.94 | CF, LD, LL, NP, SA, SY |
| Scotland | ×1.00 | AB, DD, DG, EH, FK, G, HS, IV, KA, KW, KY, ML, PA, PH, TD, ZE |
| Northern Ireland | ×0.90 | BT |
VAT
Most home improvement is standard-rated. A new dwelling built from scratch is zero-rated. A 5% rate can apply where a property has stood empty for two years or more, or where the work changes the number of dwellings — but those depend on facts about your property that we cannot check, so we assume the standard rate and tell you to ask. The trades where that is worth checking are Extension, Loft Conversion, Renovation, Plumbing.
Listed buildings do not get VAT relief. The zero rate for approved alterations to listed buildings was abolished on 1 October 2012. It is a common and expensive misunderstanding, so we would rather say it plainly than leave it out.
Contingency
Shown as its own line rather than hidden inside the rate, because it is money you hold back rather than money a builder quotes. Structural work carries 10%, fit-out work 5%, and supply-and-fit jobs where the scope is knowable up front carry none. Published UK guidance usually suggests 10–15%; we sit at the bottom of that because the range already carries a 28% high leg.
Sources
These are the sources we actually consulted when setting the rates. We do not hold a RICS or BCIS licence, and nothing here is BCIS-derived — you will see other sites claim that provenance, and we would rather tell you exactly what ours is.
- Published trade cost guides — surface & system splits
Relative pricing between surfaces/systems (driveway surfaces, flooring types, roof and plastering scopes, loft types) informing the Aug 2026 sub-type rate factors. Blended engineering judgement across public guides — not a data licence.
- HomeOwners Alliance — house extension costs
Per-m² ranges by region and storey count. Figures stated EXCLUDING VAT.
- Homebuilding & Renovating — how much does an extension cost
Per-m² by specification level, and the finding that two-storey costs LESS per m² than single-storey. Excludes VAT.
- Which? — extension costs
Contingency 10–15%, architect fees up to 10%. Which? licenses BCIS data; we do not, so this is a secondary reference.
- ONS — construction output price indices
Free, Open Government Licence, quarterly. The indexation backbone between full re-bases.
- HMRC — VAT Notice 708, buildings and construction
20% standard, 0% new dwellings, 5% for qualifying conversions and long-empty properties.
- Which? and Which? Trusted Traders — plastering and decorating costs
Per-room plastering and decorating tables. Which? states plainly that plasterers quote by room, which is why rates v4 moved plastering off an area basis.
- BookaBuilderUK — trade cost guides and day rates
Plasterer day rates by region (£180-£350) and output per day (20-30 m² of surface skimmed). The source that first showed the v3 plastering rate implied a ~£400/day plasterer.
- MyJobQuote — cost guides
Per-room and per-job tables used as a third independent anchor on plastering, decorating, flooring and window replacement.
- Checkatrade — cost guides
Per-room and per-job trade prices: bathroom, en-suite, WC, radiator fitting, window sizes, plasterer day rates. Their build-cost tables state prices exclude VAT. Their MRICS/MCIOB reviewer note is not a data licence.
- Federation of Master Builders — cost guides
Itemised window-replacement table for a 3-bed semi, and the finding that London and the South East extensions run 30–50% above national — used for the BUILD region column only.
- MyBuilder — cost guides and regional day rates
Regional builder day rates, which index London at 1.16 against a seven-city mean — an independent check on the ONS trade multiplier. Its prose claim of 20–40% above national contradicts its own table and is not used.
- Rated People — cost guides
Per-window supply-and-fit range and plasterer day rate. Cross-check only.
- ONS — ASHE Table 3, earnings by region and occupation
Median hourly pay for SOC 52 and SOC 53 by region — the basis of the TRADE region column. Employees only, and workplace-based, so it understates self-employed charge-out dispersion and attributes Home Counties trades working in London to London.
- HMRC — VAT Notice 708/6, energy-saving materials
Confirms double glazing is NOT an energy-saving material, so window replacement is standard-rated at 20%. Contradicts a widely repeated claim that 5% applies.
- MHCLG — planning fee indexation from 1 April 2026
Householder planning application fee in England: £548 from 1 April 2026.
How often this is reviewed
At least once a year, and sooner if construction costs move sharply. Our build fails automatically when the rates go past their review date, so a stale table cannot quietly stay live.