🧭 How to Read a Milestone Slip Chart (Schedule Prediction Accuracy Chart)

A Schedule Prediction Accuracy Chart—also known as a milestone slip chart—is a powerful visual tool for tracking how project milestone forecasts evolve over time. It helps teams identify schedule risks early and assess the reliability of their delivery predictions.

📊 Chart Structure

This chart, as illustrated below, is an X-Y scatter plot where:

• X-axis: Represents the date when the forecast was made (e.g., weekly status updates).
• Y-axis: Shows the forecasted completion date for a specific milestone.

Each point on the chart reflects the forecasted delivery date of a milestone at a particular time. By connecting these points over successive reporting periods, you can observe trends in schedule predictions.

📈 Interpreting the Chart

• Flat Line: Indicates consistent forecasts; the milestone’s expected completion date hasn’t changed over time.
• Upward Slope: Suggests the milestone is slipping; each new forecast predicts a later completion date.
• Downward Slope: Implies the milestone is accelerating; forecasts are moving the completion date earlier.
• Diagonal “Finish Line”: Represents the original planned schedule. Deviations from this line highlight changes in the forecast.

By analyzing these trends, project managers can assess the stability of their schedules and identify areas requiring attention.

🔍 Signs of Project Health

Understanding the patterns in a milestone slip chart can provide insights into the project’s health: