Lead

A lead is a negative lag value on a dependency relationship. If Activity A has a Finish-to-Start relationship to Activity B with a lag of −5 days, Activity B can start 5 days before Activity A finishes. Planners sometimes use leads to model fast-tracking — compressing the programme by overlapping activities that would normally be sequential. While the underlying concept of starting a successor before its predecessor is complete is entirely valid, modelling it with a negative lag is poor practice. DCMA 14 flags any negative lag as a non-compliant 'lead' and requires it to be resolved before a schedule can be accepted.

The reason leads are non-compliant is not that overlapping work is wrong — it is that negative lags are analytically unstable. They interact unpredictably with the critical path calculation, can cause incorrect float values, and make the schedule difficult to analyse and explain. The correct way to model overlapping work is with a Start-to-Start relationship combined with a positive lag where appropriate. An SS + 5-day lag is logically equivalent to a FS − 5-day lead but is analytically clean, DCMA-compliant, and clearly represents what is actually happening: Activity B can start 5 days after Activity A starts.

In schedule reviews, the presence of leads (negative lags) is often a sign that a planner has used scheduling tools to achieve a date rather than to model the work. If a critical path calculation shows a late completion, applying negative lags to key predecessors is a tempting — and illegitimate — way to compress the programme without actually changing any of the underlying work sequences or durations. A schedule full of leads should be treated with significant scepticism: the dates it shows are not the product of honest sequencing logic, and they will not materialise on site.