Which tools and techniques should a project manager use when estimating costs?

According to the PMBOK® Guide, the Estimate Costs process is the process of developing an approximation of the monetary resources needed to complete project work. This process uses a specific set of tools to ensure accuracy and consensus.

Expert Judgment and Decision Making (Choice D): These are both core Tools and Techniques for the Estimate Costs process.

Expert Judgment: Involves consulting individuals or groups with specialized knowledge in similar projects, accounting, or specific technical domains to provide insight into cost variables.

Decision Making: Specifically Voting, is used to reach a consensus among team members or stakeholders regarding the cost estimates, especially in environments where multiple perspectives are needed to finalize an approximation.

Lessons Learned Register and Cost Aggregation (Choice A): The Lessons Learned Register is an Input (specifically a Project Document), not a technique. Cost Aggregation is a tool and technique, but it belongs to the Determine Budget process, where activity cost estimates are summed up to establish a cost baseline.

Project Schedule and Resource Requirements (Choice B): Both of these are Inputs to the Estimate Costs process. The project manager looks at the schedule and resource requirements to understand what needs to be estimated, but they are not the tools used to calculate the costs.

Three-point Estimating and Risk Register (Choice C): While Three-point Estimating is a valid tool for this process, the Risk Register is an Input. The information in the risk register (such as potential threats or opportunities) informs the estimate, but it is not a technique for calculating the cost itself.

By utilizing Expert Judgment and Decision Making, the project manager ensures that the estimates are not just mathematical calculations but are tempered by professional experience and team agreement, leading to a more realistic and defensible project budget.