Lag
DE: Verzoegerung (Lag)
The amount of time a successor activity must be delayed from the predecessor.
Detailed Explanation
A lag is the amount of time by which a successor activity is required to be delayed with respect to a predecessor activity. It adds mandatory wait time between activities. Lags are always positive values and represent real constraints in the project.
Lags are typically applied to Finish-to-Start relationships. For example, after pouring concrete (predecessor), you must wait 3 days for curing before building walls (successor). This 3-day lag represents a physical constraint that cannot be compressed.
Lags should represent real-world constraints, not arbitrary buffers. Using lags as hidden schedule buffers makes the schedule unreliable and difficult to analyze. Legitimate lags include curing times, regulatory review periods, shipping durations, and other externally imposed waiting periods.
Key Points
- Mandatory wait time between activities
- Always a positive time value
- Represents real constraints (curing, shipping, review periods)
- Typically applied to Finish-to-Start relationships
- Should not be used as hidden schedule buffers
- Extends the overall schedule by the lag duration
Practical Example
In a construction schedule: after painting (5 days), there is a 2-day lag for drying before furniture installation can begin. After permit submission, a 10-day lag represents the city review period. These lags are real constraints — no amount of resources can compress them.
Tips for Learning and Applying
Only use lags for genuine constraints, not as padding
Document the reason for every lag in the schedule
Review lags periodically — some may be reducible
Distinguish lags from task duration — lags are wait time, not work time
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