Map activity logic, dates, floats, and dependencies confidently. Test lag impacts, critical chains, and timing. Keep every project milestone aligned with realistic delivery targets.
Use one activity per row. Lag is applied on the successor activity after its listed predecessors finish.
| Activity | Description | Duration (days) | Predecessors | Lag (days) |
|---|---|---|---|---|
| A | Site survey | 2 | — | 0 |
| B | Design approval | 4 | A | 0 |
| C | Material ordering | 3 | A | 1 |
| D | Foundation work | 5 | B, C | 0 |
| E | Framing | 4 | D | 0 |
| F | Inspection | 2 | E | 0 |
| G | Interior finishing | 3 | E | 0 |
| H | Final handover | 1 | F, G | 0 |
Early Start (ES) = maximum of predecessor EF + successor lag.
Early Finish (EF) = ES + Duration.
Late Finish (LF) = minimum of successor LS − successor lag.
Late Start (LS) = LF − Duration.
Total Float = LS − ES = LF − EF.
Critical Path = connected activities where total float equals zero, producing the longest controlling project duration.
Lag is the wait time inserted between linked activities. In finish-to-start logic, add lag after the predecessor finishes and before the successor starts. Example: if A ends on day 5 and lag is 2, the earliest B can start is day 7.
Create columns for Activity, Duration, Predecessors, ES, EF, LS, LF, and Float. Use formulas to compute forward pass and backward pass values. Then flag rows where float equals zero. A structured dependency table makes Excel-based CPM easier to audit.
For a construction example, list tasks like survey, design, excavation, framing, inspection, and handover. Assign durations and dependencies, then run the forward and backward pass. This page gives the solved structure; you can mirror it while recording or following any instructional video.
The critical path is the longest dependency chain controlling total project duration. Activities on this path have zero total float, so any delay on them delays the whole project unless recovery action is taken.
Float shows how much an activity can slip without delaying the project finish. It helps managers prioritize monitoring, reassign crews, and understand which tasks still have schedule flexibility.
Yes. Enter predecessor IDs separated by commas. The calculator uses the controlling predecessor finish, plus lag, to determine the earliest start for the successor activity.
The calculator checks for loops. If an activity chain points back to itself, the schedule becomes invalid and the tool returns an error asking you to fix the predecessor relationships.
No. Duration is working time for an activity. Lag is waiting time between related activities. They affect the schedule differently and should be entered separately for accurate results.
Yes. The calculator accepts decimal values, so you can model half-days, hours converted to days, or fractional working periods when your scheduling method needs more precision.
Project duration is the maximum early finish among all terminal activities. In practice, it represents the earliest possible completion time if every activity starts and finishes as planned.
Update it whenever actual durations, logic links, resource constraints, or milestone dates change. Frequent recalculation helps you catch new critical activities before they create larger delivery problems.