Provisional Sums in a Bill of Quantities
What provisional sums are, how they differ from prime cost sums, and how they affect tender comparisons.
What is a provisional sum?
A provisional sum is an allowance for work that cannot be fully defined at tender time. It holds budget and scope space until design or scope firms up.
Bidders usually add a percentage for overheads/profit on PS work where the contract allows; always read the form of contract.
Provisional sums are not a free pass to ignore scope—they should be described as clearly as the information allows, with boundaries on what is in or out.
Provisional vs prime cost
Prime cost (PC) sums often relate to supply items nominated or described but not fully priced yet, whereas provisional sums can cover whole work packages.
Misclassifying these items breaks like-for-like tender comparison.
Tender instructions sometimes define how provisional quantities are remeasured; if not, clarify whether the PS is a lump allowance or a quantity-based placeholder.
After award
As design firms up, provisional items should be converted to measured work or removed with proper documentation—otherwise budgets float without accountability.
Keep a register of which provisional items are still open at each valuation; stale PS lines are a common source of dispute at final account.