In scheduling, what is the difference between a lead and a lag?

• A. Lead and lag are the same
• B. Lead accelerates start of a successor; Lag introduces a delay
• C. Lag accelerates; Lead delays
• D. Lead accelerates the start of a successor activity; a lag introduces a delay between activities

Answer: (D)

In scheduling, the difference lies in how the next activity starts relative to the previous one. A lead means the successor can start before the predecessor finishes, creating overlap and often shortening the timeline. A lag adds a waiting period after the predecessor finishes before the successor can begin, causing a delay.

For example, you might begin wiring for a room before the drywalling is complete in that area—that’s a lead. In contrast, you might wait a day after pouring concrete before backfilling the area—there’s a lag.

This is why the best description is that lead accelerates the start of the successor, while a lag introduces a delay between activities.