---
title: "Difference between CPM and PERT"
subject: "ICT Project Management"
chapter: 8
key: "semester_7/ict_project_management:cpm-vs-pert"
source: https://www.bctengineer.com/q/semester_7/ict_project_management/cpm-vs-pert
site: BCT Engineering
---

# Difference between CPM and PERT

ICT Project Management · Chapter 8: Project Time Management

- Asked in: year not given
- Video: [PERT vs CPM| Difference between PERT and CPM| PMP | Edureka](https://www.youtube.com/watch?v=clCNKvjEN9U) — edureka!
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/ict_project_management/cpm-vs-pert
- Whole chapter: https://www.bctengineer.com/md/semester_7/ict_project_management/chapter-8

## Question

What is the difference between CPM and PERT?

## Short answer

CPM uses a single deterministic time estimate for activities, is activity-oriented, and suitable for repetitive projects. PERT uses three time estimates (optimistic, most likely, pessimistic) to calculate expected time and variance probabilistically, and is event-oriented for uncertain projects.

## Answer

**CPM (Critical Path Method)** and **PERT (Program Evaluation and Review Technique)** are network-based scheduling techniques that identify the critical path. CPM was developed in 1957 (DuPont) for construction/industrial projects; PERT was developed in 1958 (US Navy, Polaris missile) for R&D projects.

| Basis | CPM | PERT |
|---|---|---|
| Time estimate | One deterministic estimate | Three estimates: optimistic (a), most likely (m), pessimistic (b) |
| Nature | Deterministic | Probabilistic |
| Expected time | Single duration given | te = (a + 4m + b) / 6 |
| Variance | Not considered | σ² = ((b − a)/6)² |
| Orientation | Activity-oriented | Event-oriented |
| Use | Repetitive, well-known projects (construction, maintenance) | Non-repetitive, uncertain projects (R&D, new software) |
| Cost | Considers time-cost trade-off (crashing) | Mainly time; cost is secondary |
| Probability | Cannot find probability of completion | Finds probability of completing by a date using normal distribution |
| Focus | Controlling cost | Controlling time |
| Network | Activity on arrow or node | Mostly activity on arrow |
| Distribution | None | Beta distribution assumed |

#### Common points
Both use network diagrams, identify critical path and float, need a WBS and activity dependencies, and support planning and control.

#### Example of PERT numbers
a = 4, m = 6, b = 14 days: te = (4 + 24 + 14)/6 = 7 days; σ = (14 − 4)/6 = 1.67 days.

```text
CPM:  Activity -> single time -> critical path
PERT: Activity -> a, m, b -> te, variance -> probability
```

Modern software often uses CPM-style calculations with PERT estimates for uncertain tasks.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How do the time estimates of CPM and PERT differ?
   A. Both use three
   B. Both use one
   C. CPM uses one deterministic estimate; PERT uses three (a, m, b)
   D. CPM uses three; PERT uses one
   Answer: C. CPM is deterministic with a single duration; PERT is probabilistic with optimistic, most likely and pessimistic times. (Key point: Time estimates)

2. With a = 4, m = 6, b = 14 days, what is the PERT expected time te?
   A. 6 days
   B. 8 days
   C. 7 days
   D. 9 days
   Answer: C. te = (4 + 4x6 + 14)/6 = 42/6 = 7 days. (Key point: PERT expected time)

3. Which project type suits PERT best?
   A. Projects with known fixed durations
   B. Routine maintenance
   C. Repetitive, well-known construction work
   D. Non-repetitive, uncertain projects such as R&D
   Answer: D. PERT is used for uncertain, non-repetitive projects; CPM for repetitive, well-known ones. (Key point: Usage)

4. Which feature belongs to CPM rather than PERT?
   A. Variance of activity time
   B. Beta distribution assumption
   C. Finding probability of completion by a date
   D. Time-cost trade-off (crashing)
   Answer: D. CPM considers time-cost trade-off; PERT focuses on time and probability. (Key point: Cost vs probability)

## Related in other subjects

- [Difference between CPM and PERT](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Acpm-vs-pert-difference) — Project Engineering, chapter 3, asked 2×
- [Difference between CPM and PERT](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_engineering_and_management%3Adifference-between-cpm-and-pert) — Industrial Engineering and Management, chapter 3
- [Bar chart vs CPM/PERT as planning tool](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Aplanning-tool-choice) — Construction Management, chapter 2, asked 3×
- [When to use bar chart, CPM, PERT](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Abar-chart-cpm-pert-situations) — Project Engineering, chapter 3