Project Management guide · Scheduling and time
Critical Chain vs Critical Path: Key Differences Explained
The critical path is the longest chain of dependent activities, calculated assuming resources are unlimited. The critical chain is the longest chain once both dependencies and resource limits are taken into account, with safety time pulled out of individual tasks and pooled into buffers that protect the finish date.
Key takeaways
- Critical path considers dependencies; critical chain adds resource limits.
- Critical chain moves safety out of tasks into project and feeding buffers.
- Track buffer consumption against work completed.
- Choose critical chain where shared resources and multitasking cause delays.
Key differences
| Critical path method | Critical chain | |
|---|---|---|
| Considers | Activity dependencies | Dependencies and resource availability |
| Task estimates | Realistic estimates, often with hidden safety | Aggressive (focused) estimates without safety |
| Contingency | Spread across tasks or held as reserve | Pooled in project and feeding buffers |
| Tracking | Dates and float | Buffer consumption vs chain completed |
| Multitasking | Not addressed directly | Discouraged; one task at a time |
| Origin | Late 1950s | Eliyahu Goldratt, 1997, based on the theory of constraints |
How critical chain works
- Build the network and level resources so no one is double-booked; the longest resource-levelled path is the critical chain.
- Cut each task estimate to a focused, aggressive estimate, often around half of a padded estimate.
- Add a project buffer at the end of the critical chain, sized from the safety removed.
- Add feeding buffers where non-critical chains join the critical chain.
- Start tasks as soon as inputs are ready and finish them without multitasking.
- Track buffer consumption against chain progress, often on a fever chart with green, amber and red zones.
Worked example
A critical path has three tasks with padded estimates of 10, 8 and 6 days.
| Approach | Task durations | Buffer | Planned finish |
|---|---|---|---|
| Critical path | 10 + 8 + 6 = 24 days | None shown | Day 24 |
| Critical chain | 5 + 4 + 3 = 12 days | Project buffer: 50% of 12 days removed = 6 days | Day 18 |
If the critical chain is 40% complete and 2 of the 6 buffer days (33%) have been used, the project is in good shape because buffer is being used more slowly than work is completed. If 4 buffer days (67%) were already gone at 40% complete, the project manager would plan recovery action.
Pros and cons
| Critical path | Critical chain | |
|---|---|---|
| Strengths | Widely understood and supported by tools; clear dates | Accounts for resource conflicts; reduces hidden padding; simple buffer signals |
| Weaknesses | Ignores resource limits; padding is consumed by Parkinson's law and student syndrome | Needs culture change and trust; fewer tools support it; individual due dates are de-emphasised |
When to use each
- Use the critical path for most projects, especially with contractual dates per activity.
- Consider critical chain when shared resources are the main constraint, multitasking is rife, and estimates are routinely padded.
- Some organisations combine them: CPM for logic and dates, plus a visible project buffer and resource levelling.
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Frequently asked questions
What is the difference between critical chain and critical path?
The critical path considers only dependencies; the critical chain considers dependencies and resource limits, and uses buffers instead of task-level padding.
Who created critical chain project management?
Eliyahu Goldratt, who introduced it in his 1997 book Critical Chain.
What is a project buffer in critical chain?
Time added at the end of the critical chain to protect the finish date from variation in task durations.
What is a feeding buffer in critical chain?
A buffer placed where a non-critical chain joins the critical chain, so delays on the feeding chain do not hit the critical chain.
How big should the critical chain project buffer be?
A common rule of thumb is half the safety removed from tasks on the chain, though other sizing methods exist.
What is a fever chart in critical chain?
A chart that plots buffer consumed against chain completed, with zones showing when to watch or act.
What is student syndrome in critical chain thinking?
Starting work at the last possible moment, which wastes any safety built into an estimate.
How does critical chain deal with Parkinson's law?
Parkinson's law is the idea that work expands to fill the time available, so early finishes rarely get passed on. Critical chain counters it by removing padding from task estimates and pooling it in shared buffers.
Is critical chain better than critical path?
It can be in resource-constrained, multi-project environments, but it needs cultural change. CPM remains the more common approach.
Can I use critical chain in normal scheduling tools?
Some tools support it directly; in others you can add buffers as activities manually. Compare options on our tools page.