# Prime Cost Sum > Prime Cost Sum means a specified sum in the contract designated to cover the cost of work, services, goods, or materials delivered by the contractor **Term:** Prime Cost Sum **Last updated:** 2026-07-29 ## Definition ## What Prime Cost Sum Means in a Contract A Prime Cost Sum, commonly abbreviated as a PC Sum, is a provisional monetary allowance built into a contract to account for goods, services, or materials whose final cost has not yet been fixed. It is most closely associated with construction and building contracts, where certain items, such as fittings, specialist equipment, or subcontracted trades, are not selected or priced at the time the main contract is signed. Rather than leaving the price entirely open, the parties insert an estimated figure so that the overall contract sum can still be calculated and agreed. The term differs from a fixed price because it is explicitly understood to be provisional. Both parties acknowledge that the actual cost may turn out higher or lower than the sum stated, and the contract usually contains mechanisms for adjusting the final account once the true cost is known. This makes the Prime Cost Sum a budgeting and risk allocation tool as much as a pricing mechanism. In a