Prime cost sums and the adjustment nobody does
Provisional sums get adjusted because everyone knows they are placeholders. Prime cost sums look more definite, so they quietly stay in the account at the tender figure.
QScope Team · 23 April 2026 · 4 min read
A prime cost sum, usually written PC sum, is an amount included in the contract for the supply of goods or services from a supplier or specialist that the employer will select. The contractor prices its own attendance, profit and any associated builder’s work separately.
The sum itself is a placeholder. When the supplier is appointed and the actual cost is known, the placeholder comes out and the actual cost goes in.
Why it gets missed
Provisional sums announce themselves. They are explicitly for work not yet defined, and every final account checklist has a line for adjusting them.
Prime cost sums look more settled. There is a number, it relates to something specific, and it has usually been paid against in interim valuations without incident. It survives into the final account looking like a priced item rather than an unadjusted placeholder.
What the adjustment involves
Three components move, and only the first is obvious.
- The sum itself. Out at the tender figure, in at the actual cost of the goods or services supplied.
- Profit. Usually a percentage of the sum, so it moves with it. If the sum doubles, the profit allowance doubles.
- Attendance. Priced against an assumed scope of supply. If what the specialist actually does is different, the attendance may need adjusting too.
Adjusting the sum and leaving the profit and attendance at tender figures is the partial version of this error, and it is more common than not adjusting at all.
Attendance is where the argument lives
General attendance covers the things the specialist can expect on any site: access, welfare, standing scaffold, power, disposal of rubbish. Special attendance covers what a particular specialist needs: a specific craneage, a hardstanding, a temporary enclosure, out of hours access.
Special attendance is priced against a description in the bill. If the specialist appointed needs something different from what was described, that is a change to the contractor’s obligations, and it is valued accordingly.
The check at final account
List every prime cost sum in the contract bills. Against each, record the supplier appointed, the actual cost, the profit adjustment and the attendance position. Any line where the actual cost column is empty is a line nobody has closed.
It takes an afternoon on most contracts and it routinely finds money in both directions, which is the point: an unadjusted prime cost sum is as likely to be sitting in the contractor’s favour as the employer’s, and neither party benefits from an account that cannot be reconciled.
QScope carries prime cost adjustment as its own line in the final account, alongside provisional sums, so an unadjusted sum is visible rather than invisible.