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A Deep Dive into PERT Estimation

PERT: What is it?

PERT is an acronym for Program Evaluation & Review Technique, and was developed by United States Defence as a quick estimating strategy in 1950’s. It is also known as Three-Point technique or PERT Weighted Average. PERT can be used to apply to Costs, and Schedules. 


Understanding the PERT Estimation

PERT emphasis on Three-Point estimate for each Project activity incorporating Optimistic(O), Pessimistic (P), and Most Likely (M) time estimates.

The Formula to Calculate Expected Duration (TE) for an activity is 

TE = O+4M+P


This formula considers a weighted average, giving more weight to the most likely estimate. The resulting Expected Duration provides a more realistic view of the time required for an activity, considering both optimistic and pessimistic scenarios.


Key Components of PERT Estimation

Optimistic estimates (O):

The best-case scenario estimate, representing the minimum time required to complete an activity without any risks and favorable situation.

Pessimistic Estimate (P):

The worst-case scenario estimate, indicating the maximum time needed for activity completion Including Risks and an unfavorable situation.

Most Likely Time (M):

The most realistic and probable time estimate based on historical data and expert judgment, including favorable & unfavorable situations.

Let’s look at an example below. Activities Optimistic time(O)

In Days

Most likely time (M)

In Days

Pessimistic time (P)

In Days

Expected Duration

TE = (O+4M+P)/6 

In Days

1 Requirement Analysis 10 15 20 15
2 Development 20 30 40 30
3 SIT/Functional Testing 12 18 23 18
4 UAT Testing & Support 10 15 22 15
5 Production Deployment 4 6 10 6
6 Hypercare/Warranty Period 10 15 23 16
Total TE Project 100

Table 1

Note: The above Activities can be broken down into smaller tasks. I have taken an Abstract of Activities for Illustration only.


Let’s Assume the Project Start Date as 06-Dec-2023 Activities TE Start Date End Date
1 Requirement Analysis 15 06-Dec-2023 21-Dec-2023
2 Development 30 21-Dec-2023 20-Jan-2024
3 SIT/Functional Testing 18 20-Jan-2024 06-Feb-2024
4 UAT Testing & Support 15 06-Feb-2024 22-Feb-2024
5 Production Deployment 6 22-Feb-2024 28-Feb-2024
6 Hypercare/Warranty Period 16 28-Feb-2024 15-Mar-2024

Table 2

Note: Some of the above dates fall on Weekends, and this is just for Illustration Only

Now, let’s build a Timeline Chart using Table 2.


To Create the Timeline Chart in Google Sheets

  1. Select the above Table 2 (Data Range i.e Sheet1!C16:G22) in the example (Attached Google Sheet Below for Reference)
  2. Click on Insert → Select & Click on Timeline 
  3. Map the Column from Table 2 on Required fields (Settings) on the left pane to the following
    • Start Date -> Start Date
    • End Date or Duration -> End Date
    • Card Title -> Activities


Timeline Chart in Google Sheet

Link to the spreadsheet: PERT Estimation_Example

Benefits of PERT Estimation

  1. Probability Analysis: PERT estimation embraces a probabilistic methodology, offering a spectrum of potential durations for each activity. This contributes to the assessment and management of risks within the project.
  2. Improved Accuracy: PERT estimation provides a more detailed and precise depiction of project timelines when contrasted with conventional single-point estimates.
  3. Effective Resources Allocation: Project managers can better allocate resources by understanding the variability in activity durations. This promotes optimal resource utilization.
  4. Risk Mitigation: PERT estimation highlights critical path activities and potential bottlenecks, allowing project teams to focus on risk mitigation strategies.

By embracing the three-point/PERT estimation methodology, Project Managers/Sales/Developers/Testers can navigate uncertainties, enhance decision-making, and steer their teams toward successful project completion. PERT estimation is not merely a mathematical tool; it’s a strategic ally in the pursuit of project success, offering a holistic view that empowers teams to adapt, innovate, and thrive in the face of complexity.

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Sunil has 16 years of experience in BI, DWH, DB, UI testing and project delivery across Healthcare, Insurance, Banking, & Telecom industries. Currently Working with Mindset as a Project Delivery Lead, Sunil likes to learn new technologies, and follow current trends. He enjoys going on long drives, trekking, playing badminton, & listening to music.

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