Nonworking Time Calendars are one of the most misunderstood — and most important — scheduling concepts in Microsoft Project. When they are not configured correctly, project schedules can appear to behave unpredictably, with task dates shifting in ways that don’t immediately make sense.
In Microsoft Project, changing the Project Calendar alone is not enough. You must also understand how the Nonworking Time Calendars works and how it affects the visual representation of nonworking periods in the Gantt Chart.
In this article, you’ll learn what the Nonworking Time Calendars are, how it differs from the Project Calendar, and how to configure both so your schedule and Gantt Chart remain accurate and aligned.
Background: Project Calendar vs Nonworking Time Calendars
Microsoft Project uses two different calendars at the project level, and each serves a distinct purpose:
Project Calendars
The Project Calendar determines the initial scheduling of tasks before resources are assigned.
Nonworking Time Calendars
The Nonworking Time Calendar controls how nonworking periods — such as weekends and holidays — are displayed as gray shaded bands in the Gantt Chart view.
By default, Microsoft Project uses the Standard calendar for both the Project Calendar and the Nonworking Time Calendars. However, when you switch to a custom calendar (such as a holiday calendar), both settings must be updated to keep the schedule and Gantt Chart synchronized.
How to Change the Project Calendar
To change the Project Calendar to a custom calendar (such as a holiday calendar), follow these steps:
- Click the Project tab to display the Project ribbon.
- In the Properties group, click Project Information.
- In the Project Information dialog, select the desired calendar from the Calendar pick list.
- Click OK.
At this point, Microsoft Project recalculates the schedule using the selected calendar. However, nonworking periods may not yet appear in the Gantt Chart.
How to Change the Nonworking Time Calendars
To display nonworking periods correctly in the Gantt Chart, you must also update the Nonworking Time Calendar.
- Open the Timescale dialog using one of the following methods:
- Double-click the Timescale bar at the top of the Gantt Chart, or
- Double-click any gray shaded nonworking area in the Gantt Chart.
- Select the Non-working time tab.
- Choose the same calendar used for the Project Calendar.
- Click OK.
The Gantt Chart will now correctly display nonworking periods based on the selected calendar.
Conclusion
Whenever you change the Project Calendar in Microsoft Project, you should also verify the Nonworking Time Calendar setting. Keeping these two calendars aligned ensures that both the schedule calculations and the Gantt Chart visualization accurately reflect nonworking periods.
Misconfigured calendars are one of the most common causes of unexpected scheduling behavior, and correcting them is often the fastest way to restore confidence in your project plan.
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