Generally provisional sum is an amount allocated for a specialized work by a specialized firm, for which the details are not available at the time of tender. The provisional sum amount will be a best guess at the time of tender by the employer or contractor depending upon the type of provisional sum. Hence claim made by the contractor need not necessarily be the exact amount mentioned in the contract. Definition of Provisional Sum by FIDIC Conditions of Contract. Provisional Sum means a sum (if any) which is specified in the Contract as a provisional sum, for the execution of any part of the Works or for the supply of Plant, Materials or services under Sub-Clauses 13.5(Provisional Sums). Examples of provisional sums.