Bottom-up estimation, also known as detailed estimation, involves breaking down a project into smaller tasks or activities, and then estimating the time and resources required for each task. This approach allows project managers to estimate the cost and duration of the project by summing up the estimated costs and durations of all the individual tasks.
Bottom-up estimation is useful in situations where there is a high level of detail and understanding of the project, and when it is possible to break down the project into smaller tasks or activities. It is also useful when there is a high degree of certainty and when the project is complex and has many interdependencies.
An example of Bottom-up estimation would be a construction project that involves building a new office building. The project manager will break down the project into smaller tasks such as site preparation, foundation work, framing, electrical, plumbing, etc. and estimate the duration and cost of each task. Once all the tasks are estimated, the project manager can add up the individual estimates to arrive at the overall project cost and duration.
Bottom-up estimation is considered a more accurate method of estimation than analogous estimation, but it also requires more effort and resources to conduct, as it involves breaking down the project into smaller tasks and estimating each one of them. Additionally, it is also important to ensure that all the tasks are properly defined and that all the dependencies between the tasks are taken into account to get accurate results.