8.10. Bottom-up Estimating

Bottom-up estimating requires the most effort, but it is also the most accurate. As the name implies, all the detailed tasks are estimated and then combined, or "rolled up" (see Figure 8.4). Bottom-up estimating is another name for the planning model presented in Chapters 6 and 7 (see Figure 6.1). The final component of that model, building a project budget and cash flow, is described at the end of this chapter.

Within the planning model, step three calls for estimating work packages. (Recall that work packages are the lowest-level tasks on the project.) The accuracy of the entire model is dependent on the accuracy of these work package estimates. (Recall from Chapter 6 the rules for work package size and from Chapter 7 the many variables that affect work package estimates.)