What is the term for the amount added to a firm's costs for a project as part of the total fee charged?

The correct term for the amount added to a firm's costs for a project as part of the total fee charged is accurately described as operating margin. Operating margin refers specifically to the portion of a firm's revenue that remains after deducting its operating expenses, which includes costs directly associated with project execution. It serves as an important metric for evaluating the profitability of a project by showing how much of the revenue is left to cover other expenses and contribute to overall profit after operational costs.

While concepts like profit margin and cost margin also relate to profitability, they do not specifically identify the added costs in the context of firm operations in the way that operating margin does. Profit margin represents the percentage of revenue that remains after all expenses, not just operating ones, have been deducted, while cost margin is less commonly defined in industry practice and can refer to the relationship between costs and the final price charged without capturing the operational aspects of managing those costs. Revenue margin generally pertains to the total revenue generated rather than the specific costs associated with delivering a service or product.