In which stage is the accuracy of a cost estimate typically highest?

The accuracy of a cost estimate is typically highest once detailed drawings are completed. At this stage, the estimator has access to comprehensive information regarding the project, including precise dimensions, materials required, construction methods, and specific site conditions. This level of detail allows for a more accurate quantification of costs, as all elements of the project have been identified and documented clearly.

Detailed drawings serve as a definitive guide for what is to be built, significantly reducing the uncertainty that may be present in earlier phases, such as the conceptual design phase, where estimates are often based on broad assumptions and limited information. In contrast, during project execution, while actual costs can be closely monitored, they can fluctuate due to unexpected factors such as delays, changes in scope, or unforeseen issues on site. Accuracy at final project completion reflects actual costs incurred rather than estimates, making it less relevant to the question regarding estimating accuracy at initial phases.