Time Windows

Slack and Float

Slack measures schedule room. Activities with positive slack can move within their windows; activities with zero slack sit on a critical path. The point is interpretive: CPM separates work that controls the modeled finish from work that has room under the current assumptions.

highlighted = computed this step

Slack on B

Activity B has slack 1. Why: B can shift by that amount without changing the project finish. Interpretation: B is important, but it is not currently controlling the terminal finish.

SB=1S_B=1
slack tabletaskdurESEFLSLFslackA202020B325361C426260D257792E369690F29119110

Slack on D

Activity D has slack 2. Why: F is also waiting on E, so D has room in this network. The merge at F makes E the controlling predecessor instead.

SD=2S_D=2
slack tabletaskdurESEFLSLFslackA202020B325361C426260D257792E369690F29119110

No slack on C

Activity C has slack 0. Why: any delay on C reaches the terminal finish through E and F. Zero slack is the local signal that an activity lies on a critical route.

SC=0S_C=0
slack tabletaskdurESEFLSLFslackA202020B325361C426260D257792E369690F29119110

Diagram note

Slack equals latest start minus earliest start, recomputed exactly for every activity. It measures modeled schedule room; it does not include staffing limits, calendar rules, or uncertainty. Pixel positions are rounded for layout; every number shown is exact.

Si=LSi−ESiS_i=LS_i-ES_i
slack tabletaskdurESEFLSLFslackA202020B325361C426260D257792E369690F29119110