Planning and Scheduling: Estimating Work and Costs
Quick Summary
A guideline on how to estimate effort, duration, and costs for items in the work breakdown structure (WBS). It includes a table used for assigning task estimates. Fourth in a series—see the Related Templates below for the others.
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What this is
This is the fourth in a series of templates for project plan and schedule development. This template describes the process of estimating the work effort and duration for items in the WBS, as well as estimating costs for each item to feed the project budget. Although strictly speaking cost estimating is not part of the "scheduling process," in reality the schedule can't be considered complete without eventually optimizing it for the best balance for the project between scope, time, and resources/costs. Therefore, we've addressed cost estimating in this step of the planning process.
Estimating tasks should be done after the first pass of identifying task dependencies, so that any task repartitioning resulting from identified dependencies has already been done.
Why it's useful
Estimation should be done very visibly, with the active involvement of the people who will actually be executing the work. The person responsible for delivering an activity must commit to the work and cost estimates. These people know at the working level what it takes to get the job done, what their work environment is like, what tools and other supporting resources are needed, and how that will all affect the work time and costs to get the job done. Estimating work for each item in the WBS helps ensure the schedule develops methodically based on the hours or work truly required, rather than through top-down guesses on activity durations.
How to use it
- Involve the team in the estimating process. Talk about how to ensure good estimates so that the team will eventually build a schedule everyone can believe in and support. Review key guidelines from this file to ensure that people are using consistent estimating approaches and assumptions.
- Identify what functional managers may want to take part, to provide inputs or sanity checks.
- Decide how to use the worksheet included in this template to capture information—for example, having individuals record estimates for their own activities, having sub-teams estimate and review a major section of the WBS, etc.
- If you're already entering information right into a scheduling tool, define how information will be collected and/or entered into the tool.
As you estimate durations, keep in mind the following distinction between duration, effort, and calendar time:
- Effort is the person-hours required to complete a tasks, without considering any slack time, waiting, non-working days or other delays. Effort (first-order approximation) is independent of the number of people working on a task.
- Duration is the number of hours to complete a task, taking the number of resources into account. Thus (first-order approximation) a task with a duration of 4 days with one resource will have a duration of 2 days with two resources.
- Calendar time is the time it will take to do a task, considering work hours, holidays, slack time, waiting, etc.
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