Bottom-Up Estimating

Bottom-Up Estimating is a method of estimating the duration, cost, or required resources for a project by aggregating estimates from the lower-level components of the Work Breakdown Structure (WBS). This approach provides high accuracy by analyzing each task individually and rolling up the estimates to determine overall project requirements.

Key Aspects of Bottom-Up Estimating

• Detailed & Accurate – Estimates are based on individual work components.
• Builds from the WBS – Starts with the smallest tasks and aggregates upwards.
• Time-Consuming but Precise – Requires thorough task analysis but produces reliable estimates.
• Supports Resource Planning – Helps allocate time, cost, and materials accurately.

Steps in Bottom-Up Estimating

1. Break Down the Work – Identify all tasks and subtasks in the WBS.
2. Estimate Each Component – Determine time, cost, and resources required for each task.
3. Aggregate Estimates – Roll up individual estimates to higher-level components.
4. Validate & Adjust – Review total estimates for feasibility and accuracy.

Example Scenario

A software development project requires estimating the effort to complete a Login Feature. The estimation follows a bottom-up approach by breaking the feature into smaller components.

Mermaid Diagram: Bottom-Up Estimating Example

graph TD;
    Project["Total Login Feature Estimate"] -->|Sum of all estimates| Dev["Development (10 days)"]
    Project -->|Sum of all estimates| QA["Testing (5 days)"]
    Project -->|Sum of all estimates| PM["Project Management (3 days)"]
    
    Dev -->|Frontend: 4 days| FE["Frontend Development"]
    Dev -->|Backend: 6 days| BE["Backend Development"]
    
    QA -->|Test Cases: 2 days| TC["Write Test Cases"]
    QA -->|Execution: 3 days| TE["Execute Tests"]

Calculated Estimate

Task	Duration
Frontend Development	4 days
Backend Development	6 days
Writing Test Cases	2 days
Executing Tests	3 days
Project Management Oversight	3 days
Total Estimated Duration	18 days

Why Bottom-Up Estimating Matters

• Improves Estimate Accuracy – Reduces risk by considering all work components.
• Enhances Resource Planning – Ensures proper allocation of labor, materials, and costs.
• Supports Risk Management – Identifies task-level risks before rolling up estimates.
• Increases Stakeholder Confidence – Provides detailed estimates backed by task-level analysis.

See also: Analogous Estimating, Parametric Estimating, Program Evaluation and Review Technique (PERT), Multipoint Estimating.