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A project schedule combines activities, dependencies, duration estimates and resource availability. The critical path constrains the earliest finish under the stated schedule assumptions.

About 3 min to read · Take extra time for practice · AI-assisted learning notes · Expanded October 17, 2026

First, the key terms.

Dependency: A relationship constraining the order of activities.
Float: Schedule flexibility before an activity delays the relevant finish under the model.
Crashing: Adding resources or cost to shorten suitable activities.

The idea, explained

An effort estimate is not a calendar duration. A task needing 20 hours of work may span several days if a specialist is available only part time. Dependencies determine which work can start; resource constraints can create additional delays. Estimates should identify assumptions and uncertainty rather than imply that a single number is certain. Microsoft Project and similar tools can calculate dates from a model, but accurate calculations cannot repair incorrect dependencies, calendars or capacity inputs.

STEP 1

Build the network

Translate WBS packages into activities and justified dependencies. Distinguish unavoidable technical order from habitual sequencing. Record working calendars, external lead times and available resources so the network reflects how work can actually happen.

STEP 2

Find the constraint

Compare complete dependency paths. The longest-duration path constrains finish in a basic unconstrained network. A short activity can be critical if it has no float; a long one may have flexibility. Recheck after any change.

STEP 3

Shorten responsibly

Fast-tracking overlaps work, increasing rework or coordination risk. Crashing adds suitable capacity, often at extra cost. Resource leveling may extend finish to resolve over-allocation. Protect quality, safety and sustainable human workload rather than compressing every estimate.

Follow a worked example.

After a two-day data-access task, labeling takes four days while interface work takes three days. A final one-day integration task needs both branches. Assume unlimited suitable resources, whole working days and no other dependencies.

Walk it through, one step at a time

The labeling path totals 2 + 4 + 1 = 7 days. The interface path totals 2 + 3 + 1 = 6 days. The earliest modeled finish is seven days.
Reducing interface work by a day does not shorten that finish. Reducing labeling by one day may, if all other assumptions hold.
If the same analyst must do both branches sequentially, the unlimited-resource estimate no longer applies. Update assignments and recompute dates in the scheduling tool.

Where people get stuck

More people do not automatically reduce a task’s duration proportionally; coordination, indivisible work and learning time can offset gains.

Now try it yourself.

Pause before opening each answer. Explain your reasoning in your own words.

1. Check the core idea

Why might a schedule with valid task dependencies still be impossible?

Reveal the answer & reasoning

It may allocate the same resource to simultaneous work beyond available capacity or omit calendars, external delays and practical constraints.

2. Apply what you learned

Would shortening a noncritical activity always improve the project finish?