Prime Cost Sum (PC Sum)

A prime cost sum - commonly abbreviated to PC sum or simply PC - is a provisional allowance written into a construction contract or bill of quantities. It represents the anticipated cost of a specific element of work or supply where the client intends to nominate the subcontractor or supplier themselves, rather than leaving that selection to the main contractor. Because the client has not yet settled on their preferred specialist at tender stage, the PC sum acts as a placeholder that is later adjusted once the nominated party's actual price is confirmed.

How PC Sums Work in Practice

The main contractor prices their tender around the PC sum as stated in the contract documents. They do not source or competitively price this element themselves - they accept the allowance and add separately for attendance (covering site coordination, welfare provision, scaffold access, and on-site management of the nominated subcontractor) and profit. Once the client nominates the subcontractor and that subcontractor's price is agreed, the contract sum is adjusted: if the actual cost exceeds the PC sum, the contract sum increases by the difference; if it comes in lower, the saving flows back to the client.

PC sums most commonly appear for specialist elements such as lifts, bespoke mechanical and electrical systems, specialist joinery, or high-specification fixtures that a design team has specified. The cost consultant or quantity surveyor typically establishes the PC sum amount using benchmark pricing at the time of tender, with the expectation that it will be reconciled once the nominated subcontractor is appointed.

PC Sum vs. Provisional Sum

A prime cost sum and a provisional sum are often confused but serve different purposes. A PC sum is specifically for work to be carried out by a nominated party - the client's selection of the supplier or subcontractor is what defines it. A provisional sum is a broader allowance for work that is undefined at tender stage, which the main contractor will typically price and carry out themselves or subcontract domestically once the scope is confirmed.

The key practical difference is accountability. Where a nominated subcontractor causes delay or additional cost, the responsibility between client and main contractor is more complex than for domestic subcontracting. Modern standard forms such as JCT 2016 have moved away from formal nomination in many situations, replacing it with named subcontractor procedures that place clearer performance responsibility with the main contractor. PC sums remain in use, particularly on bespoke or complex projects where a specialist has been involved in the design and the client wants to carry that relationship into the build phase.