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 vs Fixed Fee (2026)
How the two pricing models compare for a typical home extension.
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.
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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