Network Logic
Deterministic critical path scheduling — predecessor types, lag, constraints, and float calculation.
ProjectXL implements a full deterministic scheduling engine inside Excel. This is not Gantt chart rendering — the engine computes early start, early finish, late start, late finish, total float, and free float across your entire network using standard CPM algorithms.
Predecessor Types
The engine supports all four standard relationship types:
- Finish-to-Start (FS) — the successor cannot start until the predecessor finishes
- Start-to-Start (SS) — the successor cannot start until the predecessor starts
- Finish-to-Finish (FF) — the successor cannot finish until the predecessor finishes
- Start-to-Finish (SF) — the successor cannot finish until the predecessor starts
Each relationship supports positive and negative lag values.
Constraint Logic
Activities can carry date constraints that interact with the scheduling logic:
- As Soon As Possible — default, no constraint
- Start No Earlier Than — prevents the activity from being scheduled before a specific date
- Finish No Later Than — flags or forces completion by a target date
Constraint violations are surfaced in the validation panel, not silently absorbed.
Calendar Integration
Every activity is scheduled against a specific calendar. The engine respects working days, holidays, and custom shift patterns when computing durations and dates.
Float Calculation
Total float and free float are computed for every activity in the network. Float values drive critical path identification and schedule sensitivity analysis. The engine distinguishes between:
- Total Float — the amount of time an activity can slip without delaying the project finish
- Free Float — the amount of time an activity can slip without delaying any successor