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What is a provisional sum?

A provisional sum is an allowance included in the contract for work that cannot be fully described or priced at tender stage. It is adjusted up or down against the actual cost once the work is defined and executed.

Provisional sums are common for items like site clearance, rock excavation, or kitchens and sanitaryware not yet chosen. A prime cost sum is similar but relates to the supply of a specific item where the price is not yet known.

A tender full of provisional sums is not a fixed price. Compare tenders on the fixed element as well as the total, and pin down the big allowances as early as possible.

Where they usually appear

  • Ground conditions and rock breaking
  • Wastewater treatment system and percolation area
  • Kitchen, wardrobes and sanitaryware supply
  • External works and landscaping

Sources

Last reviewed 28 August 2026. General information only — not legal or planning advice.

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