Extension Builders: Day Rate vs Fixed Fee (2026 UK)
Should you pay your extension builder a day rate or agree a fixed price? A day rate runs about £150–£250 per day per skilled tradesperson in 2026 and suits small or hard-to-define jobs. A fixed-fee contract protects your budget on a clearly-specified extension but needs detailed drawings first. For most full extensions, a fixed price is the safer choice — this guide compares both, with the pros, cons and when each wins.
Day rate explained Fixed price explained Which to choose
Use a day rate (£150–£250/day per tradesperson) for small, exploratory or hard-to-specify work where the scope may change. Use a fixed price for a fully-designed extension so you know the total cost upfront and the risk of overruns sits with the builder. Most full extensions should be priced on a fixed-fee contract backed by a detailed spec.
Side by Side
Day Rate vs Fixed Fee (2026)
How the two pricing models compare for a typical home extension.
Factor
Day rate
Fixed fee
Typical cost
£150–£250/day each
Agreed lump sum
Budget certainty
Low
High
Who carries the risk
You
The builder
Best for
Small / undefined work
Fully-designed projects
Needs detailed spec?
No
Yes
Rule of thumb in 2026: the more clearly you can define the job, the more a fixed price works in your favour — it transfers the risk of delays and overruns to the builder.
Pros & Cons
When Each One Wins
Day rate — flexible but open-ended. Ideal for small jobs, snagging or work where you can't fully define the scope. The downside is no cost ceiling, so it rewards a builder who works slowly.
Fixed fee — predictable but rigid. You know the total before work starts and the builder absorbs overruns. The trade-off is that changes mid-build (variations) are charged on top, often at a premium.
Watch out for vague quotes. A fixed price is only as good as the spec behind it. Make sure drawings, materials and a finishes schedule are agreed so you compare like with like.
Stage payments protect you. On a fixed-fee extension, tie payments to completed stages rather than paying large sums upfront.
Hybrid is common. Many extensions are a fixed price for the main shell with a day-rate allowance for groundworks or unknowns uncovered during the dig.
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A skilled tradesperson typically charges £150–£250 per day in 2026, with labourers at £100–£150. Rates are higher in London and the South East. On a day rate you also pay for materials and any plant or skip hire on top.
For a fully-designed extension, yes — a fixed price gives budget certainty and puts the risk of overruns on the builder. A day rate is better only for small or undefined work where you can't write a clear specification.
A detailed specification and drawings. A fixed price only holds if the scope is locked down; any change you request (a variation) is charged on top. Agree a written variations process and a clear finishes schedule before work starts.
Avoid large upfront payments. On a fixed-fee extension, tie payments to completed stages (foundations, walls, roof, fit-out) and hold a small retention until snagging is finished. A modest deposit to secure materials is normal; paying for most of the job in advance is not.
Yes, and it's common. Many extensions are priced as a fixed sum for the main build with a day-rate allowance for groundworks or unknowns found during excavation. This keeps most of the cost fixed while allowing for genuine surprises.
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