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27 January 2011

Fine-tuning Task Relationships with Lead and Lag

David A. Zimmer Print

PMBOK® Guide Definition:

Lag: A modification of a logical relationship that directs a delay in the successor activity. For example, in a finish-to-start dependency with a ten-day lag, the successor activity cannot start until ten days after the predecessor activity finishes. See also lead.

Lead: A modification of a logical relationship that allows an acceleration of the successor activity. For example, in a finish-to-start dependency with a ten-day lead, the successor activity can start ten days before the predecessor activity has finished. A negative lead is equivalent to a positive lag. See also lag.

Practical Definition:

Lag: A pre-defined delay between the predecessor and successor activities, as in, the delay caused by paint drying before picture hanging.

Lead: A pre-defined acceleration of the successor activity in relationship to the predecessor relationship, also known as, negative lag. Used to create overlap of tasks to shorten the overall length of the project.

Understanding Lead and Lag

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