Critical path calculator: find the CPM path and total float
Type your activities, durations and finish-to-start predecessors. The forward pass, backward pass, total float and critical path recalculate on every keystroke — no sign-up, nothing leaves your browser. It loads with the 9-task website migration example from the Gantt vs critical path guide so you can experiment before entering your own schedule.
1. Your task list
| Code | Task | Duration (days) | Predecessors | Remove |
|---|---|---|---|---|
Schedule summary
Project duration
33days
Critical path
A → B → C → E → H → I
3 of 9 tasks carry float and can slip without moving the finish date.
2. Forward pass, backward pass and float
| Task | Dur | ES | EF | LS | LF | Float | Critical |
|---|---|---|---|---|---|---|---|
| AContent audit | 5 | 0 | 5 | 0 | 5 | 0 | Critical |
| BInformation architecture | 4 | 5 | 9 | 5 | 9 | 0 | Critical |
| CVisual design | 8 | 9 | 17 | 9 | 17 | 0 | Critical |
| DContent rewrite | 10 | 9 | 19 | 12 | 22 | 3 | slack 3d |
| EFront-end build | 9 | 17 | 26 | 17 | 26 | 0 | Critical |
| FCMS setup & data model | 6 | 9 | 15 | 16 | 22 | 7 | slack 7d |
| GContent load | 4 | 19 | 23 | 22 | 26 | 3 | slack 3d |
| HIntegration & QA | 5 | 26 | 31 | 26 | 31 | 0 | Critical |
| ICutover & DNS switch | 2 | 31 | 33 | 31 | 33 | 0 | Critical |
3. Schedule view
Solid bars are the early schedule. The lighter tail shows available float.
- A Content auditd0–5
- B Information architectured5–9
- C Visual designd9–17
- D Content rewrited9–19
- E Front-end buildd17–26
- F CMS setup & data modeld9–15
- G Content loadd19–23
- H Integration & QAd26–31
- I Cutover & DNS switchd31–33
How to read the numbers
- ES / EF (early start, early finish)
- The soonest a task can start and finish once every predecessor is done. Day 0 is the project start.
- LS / LF (late start, late finish)
- The latest a task can start and finish without pushing the project completion date.
- Total float
- LS minus ES — how much a task can slip before it starts costing the project. Zero float means the task is on the critical path.
Frequently Asked Questions
How is the critical path calculated in this tool?
The calculator runs a forward pass (to find Early Start and Early Finish) and a backward pass (to find Late Start and Late Finish). Tasks with zero total float (LS − ES = 0) form the critical path.
What does total float mean?
Total float is the amount of time a task can be delayed without delaying the overall project finish date. It is calculated as Late Start − Early Start (or Late Finish − Early Finish).
Can I use finish-to-start predecessors only?
Yes. This calculator currently supports classic finish-to-start (FS) relationships, which cover the large majority of project schedules. Enter the predecessor task codes in the Predecessors column.
Is my data stored or sent anywhere?
No. Everything runs entirely in your browser. Nothing is saved or transmitted to any server.
How do I export the results?
Use the “Export CSV” button above the float table. It downloads the full schedule with ES, EF, LS, LF, float and critical-path flags.
What’s the difference between total float and free float?
Total float protects the project end date. Free float protects the early start of the next task. This calculator shows total float. You can read the detailed comparison in the related guide “Total Float vs Free Float”.
Read the guide: Total Float vs Free Float
Related guides
Go deeper on the scheduling maths this calculator runs.
- PlanningCritical Path Analysis: Steps, Float Formula & ExampleCalculate the critical path and total float, then turn the schedule into a realistic project plan with scope, capacity, risk, acceptance and change controls. 18 min read
- People & DeliveryStakeholder Analysis: Power/Interest Grid + Comms PlanIdentify, analyse and engage stakeholders: power/interest and salience models, an engagement assessment matrix, a communication plan, tactics for resistance and a worked example. 14 min read
- PlanningTotal Float vs Free Float: The Difference, With ExamplesTotal float protects the project end date; free float protects the next task. Worked numbers showing why confusing the two costs you weeks. 7 min read
Guides behind the Critical Path Calculator
- How to calculate the critical path and total floatForward pass, backward pass and the LS − ES formula, worked end to end.
- Critical path method example, step by step with numbersA full worked network you can re-enter in the calculator.
- Total float vs free float explainedWhich float delays the project and which only delays the next task.
- Gantt chart vs critical path: the 9-task example behind this toolThe example the calculator loads by default.
- Estimating task durations before you scheduleBetter durations in, a more trustworthy critical path out.