---
title: "Difference between CPM and PERT"
subject: "Project Engineering"
chapter: 3
key: "semester_7/project_engineering:cpm-vs-pert-difference"
source: https://www.bctengineer.com/q/semester_7/project_engineering/cpm-vs-pert-difference
site: BCT Engineering
---

# Difference between CPM and PERT

Project Engineering · Chapter 3: Project Planning and Scheduling

- Asked in: 2082 Baisakh, 5 marks; 2080 Baisakh, 4 marks (asked 2 times)
- Video: [PERT Vs CPM: Difference between them with definition & Comparison Chart](https://www.youtube.com/watch?v=dFTG3ohAcso) — Key Differences
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/project_engineering/cpm-vs-pert-difference
- Whole chapter: https://www.bctengineer.com/md/semester_7/project_engineering/chapter-3

## Question

Differentiate between CPM and PERT.

## Short answer

CPM uses a single deterministic duration and is activity-oriented, allowing time-cost trade-off. PERT uses three time estimates (optimistic, most likely, pessimistic) to compute expected time and is event-oriented, suitable for projects with high uncertainty.

## Answer

| Basis | CPM | PERT |
|---|---|---|
| Full form | Critical Path Method | Programme Evaluation and Review Technique |
| Origin | DuPont, 1957, construction and plant maintenance | US Navy, 1958, Polaris missile project |
| Time estimate | One deterministic time | Three times: optimistic $a$, most likely $m$, pessimistic $b$ |
| Nature | Deterministic | Probabilistic |
| Expected time | Given duration | $t_e = \dfrac{a + 4m + b}{6}$ |
| Basis | Activity oriented | Event oriented |
| Cost | Time-cost trade-off (crashing) considered | Mainly time; cost not usually considered |
| Suitable for | Repetitive, known work (construction) | Research, development and new projects with uncertainty |
| Output | Critical path and float | Critical path and probability of finishing by a date |
| Network | Activity-on-arrow or activity-on-node; dummies needed only in activity-on-arrow | Event-based activity-on-arrow network; dummies used where needed |

## Check yourself

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

1. PERT uses how many time estimates?
   A. One
   B. Two
   C. Three
   D. Four
   Answer: C. Optimistic, most likely and pessimistic. (Key point: Time estimate)

2. Expected time in PERT:
   A. (a+m+b)/3
   B. (a+4m+b)/6
   C. (4a+m+b)/6
   D. (a+b)/2
   Answer: B. te = (a + 4m + b)/6. (Key point: Expected time)

3. CPM is:
   A. Probabilistic
   B. Deterministic and considers time-cost trade-off
   C. Event-based without cost
   D. For research only
   Answer: B. CPM uses one duration and considers crashing. (Key point: Nature)

4. PERT suits:
   A. Repetitive known work
   B. Research and new projects with uncertainty
   C. Maintenance only
   D. Bar charts
   Answer: B. PERT is probabilistic and gives probability of finishing by a date. (Key point: Suitability)

## Related in Project Engineering

- [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
- [CPM and PERT and their uses](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Acpm-pert-uses) — Project Engineering, chapter 3
- [CPM vs PERT; te and variance for x, y](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Acpm-pert-te-variance-x-y) — Project Engineering, chapter 3

## Related in other subjects

- [Difference between CPM and PERT](https://www.bctengineer.com/question.md?key=semester_7%2Fict_project_management%3Acpm-vs-pert) — ICT Project Management, chapter 8
- [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×