Bottom up estimating is a method of project cost estimation that involves estimating the cost of individual tasks at the lowest level of the work breakdown structure and aggregating them up through each level. It is most accurate when the project has a detailed work breakdown structure and activity list, and when the resources required for each activity are known. The advantages include high accuracy, reliability, ability to see impact of changes, and enabling detailed tracking and control. The approach involves assigning resources to work packages, calculating package costs, and rolling the estimates up through the WBS levels to the overall project level.

1. What is
bottom up
estimating?

2. Bottom up
estimating
is a form of project
estimating for cost,
resource and duration

3. A definition...

4. Estimate derived by first
estimating the cost of the project’s
elemental tasks at the lower levels
of the WBS and then aggregating
those estimates at successively
higher levels.
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Dictionary of Project Management Terms, 3rd Edition,
J. LeRoy Ward

5. What?
It uses detailed estimates for
small chunks of the project and
adds them together

6. Bottom up
estimating
is used when...

7. 1. You have a detailed
Work Breakdown
Structure (WBS)
2. You have an
activity list

8. 3. You know the
resources required
for each activity

9. Advantages
• It is the most accurate form of
estimating
• It is the most reliable
• It makes it easier to see the
impact of changes later on
• It enables detailed tracking and
better project control

10. Approach
• Assign the resources to work packages
• Calculate the cost of the work packages
• Roll up all the estimates to the
intermediate level of the WBS
• Roll up the estimates to the project level

11. Bottom up
estimating
provides solid estimates
when you have
a detailed plan

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