Scheduling Fundamentals
Baseline Schedule
The baseline schedule is the originally approved project schedule, used as the fixed reference point every later update is measured against to identify delay.
Definition
A baseline is a snapshot of the schedule -- typically the one agreed to at contract award or notice to proceed -- that gets locked in as the point of comparison for the life of the project. As the project progresses and the schedule gets updated, planned dates in the current update are compared back against the baseline's dates to see how far activities have actually shifted. Without a baseline, there's no fixed reference point to measure delay against; every comparison would only show change between two arbitrary updates rather than deviation from the original plan.
Example
A project's baseline shows 'Substantial Completion' planned for October 1. The current update forecasts November 15 -- a 45-day slip from baseline that then needs to be attributed to specific causes and activities.