How to Account for Holidays in Microsoft Project

You build a clean project schedule. Tasks line up perfectly. Deadlines look achievable. Then a national holiday hits — and the whole thing shifts. Suddenly your team is “working” on days they’re not even in the office, and your timeline becomes fiction.

This is one of the most common and most avoidable scheduling mistakes in Microsoft Project. The good news: accounting for holidays takes less than 10 minutes once you know where to look. The bad news: most people never learn this until a deadline is already missed.

This guide walks you through exactly how to do it — step by step — so your schedules reflect real working days, every time.

Why Holiday Planning Wrecks More Projects Than You Think

Project delays are not just about poor planning or unrealistic timelines. A huge chunk of scheduling failures trace back to something far simpler: calendars that don’t reflect when people actually work.

According to the Project Management Institute (PMI), $97 million is wasted for every $1 billion invested in projects due to poor project performance. A significant portion of that waste ties directly to inaccurate scheduling. PMI also found that only 47% of projects are delivered within their original budget, with schedule miscalculations being one of the top contributing factors.

The Standish Group’s CHAOS Report shows that 52.7% of projects cost nearly 189% of their original estimates — a staggering overrun that scheduling errors compound heavily.

When Microsoft Project doesn’t know your team is off for a national holiday, it schedules work on that day anyway. That single miscalculation can cascade into missed dependencies, wrong resource calculations, and deadlines that feel completely off — because they are.

The fix is not complex. It’s just a setting most people skip.

How Microsoft Project Handles Calendars

Before jumping into the steps, it helps to understand how Microsoft Project thinks about time.

Microsoft Project uses three layers of calendars to control when work can happen:

Base Calendar — The master template. Microsoft Project ships with three built-in base calendars: Standard (Mon–Fri, 8am–5pm), 24 Hours, and Night Shift. Every project and resource inherits from one of these unless you customize it.

Project Calendar — Applied at the project level. This controls the default working times for the entire project schedule and is usually built on top of a base calendar.

Resource Calendar — Applied to individual team members. This lets you override the project calendar for specific people — useful when one person is on leave, works part-time, or is in a different country with different holidays.

Holiday settings live inside these calendars. When you mark a date as non-working in the base calendar, Microsoft Project stops scheduling work on that day across the entire project.

How to Add Holidays to Your Microsoft Project Calendar

Open the Change Working Time Dialog

This is your control panel for all calendar settings.

Go to the Project tab in the ribbon, then click Change Working Time inside the Properties group.

Alternatively, navigate to File → Options → Schedule, then click the Change Working Time button at the bottom.

A dialog box will open showing a visual calendar and the working time configuration for whichever calendar is currently selected.

Select the Right Calendar to Edit

At the top of the Change Working Time dialog, you’ll see a dropdown labeled “For calendar.” This shows the currently selected calendar.

If you want to apply holidays to your entire project, select the base calendar your project uses — typically Standard. Any changes you make here will apply project-wide.

If you want to apply holidays to a specific resource only, look for that person’s name in the dropdown. Microsoft Project creates individual resource calendars automatically when you add resources to your project.

Navigate to the Holiday Date

Use the visual calendar in the dialog to click on the date you want to mark as a holiday. You can navigate months using the left and right arrows at the top of the calendar.

Click directly on the date — for example, December 25th.

Add an Exception for That Date

Once you’ve clicked a date, go to the Exceptions tab at the bottom of the dialog box.

Click in an empty row in the Name column and type a label for the holiday — for example, “Christmas Day” or “Independence Day.” Press Enter.

The Start and Finish columns will automatically populate with the date you selected. If the holiday spans multiple days (like a multi-day company shutdown), change the Finish date accordingly.

Set the Exception as Non-Working

By default, the exception may still show as a working day. Click Details on the right side of the Exceptions tab to open the exception details.

In the Details dialog, select “Non-working” under “Set day(s) to.” Click OK to confirm.

The date will now appear shaded in gray on the calendar, indicating it has been flagged as a non-working day. Microsoft Project will no longer schedule tasks on that date.

Click OK to close the Change Working Time dialog and save your settings.

Repeat for All Public Holidays

Most projects span multiple months, which means multiple holidays. Repeat the steps above for each holiday relevant to your project:

• National public holidays
• Company-wide shutdown days
• Regional or local holidays your team observes
• Bridge days around long weekends

This one-time investment pays off every time a task touches a holiday period and Microsoft Project automatically shifts it to the next working day.

How to Create a Custom Holiday Calendar

If you manage recurring projects or have a standard set of holidays every year, building a reusable custom calendar saves significant time.

Create a New Base Calendar

Inside the Change Working Time dialog, click Create New Calendar.

A dialog will appear asking you to name the calendar and choose whether to create it from scratch or base it on an existing calendar. Select “Make a copy of [Standard] calendar” — this preserves your standard working hours so you only need to add the holiday exceptions on top.

Name it something clear and specific: “US Holidays 2025” or “Company Calendar — APAC” works well.

Add All Your Holiday Exceptions

Follow the same exception steps described above — navigate to each holiday date, add a labeled exception, and mark it as non-working.

Assign the Custom Calendar to Your Project

Once your custom calendar is built, go to Project → Project Information. In the dialog that opens, find the Calendar dropdown and select your newly created calendar.

Every task in your project will now respect the non-working dates in that calendar.

How to Assign Calendars to Individual Resources

Sometimes your team members observe different holidays — a team in India has different public holidays than a team in the United States. Resource-level calendars solve this.

Open the Resource Sheet

Switch to the Resource Sheet view by going to View → Resource Sheet.

Access Resource Information

Double-click on any resource name to open the Resource Information dialog. Navigate to the Working Time tab.

You’ll see a calendar specific to that resource, already based on the project’s base calendar by default.

Change the Base Calendar for That Resource

In the dropdown labeled “Base calendar,” select whichever calendar is appropriate for that person — whether it’s an existing base calendar or the custom holiday calendar you just created.

You can also add individual exceptions directly here, just like you did with the project-level calendar.

Click OK to save.

Now, Microsoft Project will schedule that resource’s work according to their specific working time — including their regional holidays — without affecting the rest of the project.

How to Apply a Task Calendar for Holiday-Specific Scenarios

In some cases, certain tasks cannot happen on holidays regardless of resource availability — client-facing deliveries, regulatory submissions, or systems deployments during maintenance windows.

Assign a Calendar to a Specific Task

Open the task by double-clicking it to bring up Task Information. Navigate to the Advanced tab.

Under Calendar, select the appropriate calendar from the dropdown.

There’s also a checkbox labeled “Scheduling ignores resource calendars.” If you check this, the task follows only its assigned calendar — overriding even the individual resource calendar. Use this carefully, as it can override your resource’s non-working time settings.

Common Mistakes That Throw Off Your Holiday Settings

Even once you know how to set holidays, a few traps catch people repeatedly.

Editing the wrong calendar level. Adding a holiday to the Standard base calendar affects all projects that use Standard. If you only want to affect one project, create a custom calendar and assign it at the project level instead of editing the global base calendar.

Forgetting to update the calendar each year. Recurring projects need recurring calendar updates. Build a habit of reviewing and updating your holiday calendar at the start of each new project or fiscal year.

Missing regional differences. If your team spans multiple countries, using one calendar for everyone creates invisible errors. Use resource-level calendars to assign the right regional holidays to the right people.

Not checking existing tasks after adding holidays. When you add a new holiday exception after tasks are already scheduled, Microsoft Project recalculates task dates. Review your schedule after making calendar changes to catch any unexpected shifts.

Using the 24 Hours calendar for standard projects. The 24 Hours calendar never has non-working time — holiday exceptions won’t apply to it. Stick with Standard for typical weekday-based projects.

What the Data Says About Project Schedule Failures

The numbers make a compelling case for getting this right.

According to KPMG’s Global Project Management Survey, 70% of organizations have suffered at least one project failure in the past 12 months. Scheduling inaccuracy ranks among the top three causes cited.

Research by Wellingtone found that only 22% of organizations have a project management culture — meaning most teams are still improvising their way through scheduling decisions, including holiday planning.

The Harvard Business Review reports that large IT projects run 45% over budget on average and 7% over time, while delivering 56% less value than predicted. A material chunk of these overruns stems from timeline errors that compound across months of execution.

On the flip side, organizations with disciplined project management practices are 2.5 times more likely to complete projects on time and within budget, according to PMI’s Pulse of the Profession.

Getting your holiday calendar right is a small act with an outsized impact on schedule accuracy. It’s the kind of foundational setup that separates projects that land on time from projects that constantly explain why they didn’t.

Pro Tips for Keeping Holiday Calendars Clean and Accurate

Build your holiday calendar before you build your schedule. Set up all non-working days first, then let Microsoft Project calculate your task durations. This prevents you from having to manually reschedule tasks after adding exceptions late.

Use descriptive exception names. “Holiday” is not useful six months from now. Name exceptions specifically: “Thanksgiving (US) — Nov 2025” or “Company All-Hands Day.” It makes audits and calendar reviews far easier.

Document your calendar logic. Keep a simple spreadsheet or note that lists which projects use which calendars and why. When a new team member takes over, they won’t have to reverse-engineer your settings.

Test your calendar with a dummy task. After adding holiday exceptions, create a short test task that spans the holiday period. Check that Microsoft Project skips the non-working day and schedules the task correctly before you commit to the full build.

Export your custom calendars. Microsoft Project lets you copy calendars from one project to another using the Organizer (go to File → Info → Organizer). Store your best calendar builds in your global.mpt file so they’re available in every new project.

Start with your next project. Before you add a single task, set your calendar. Your future self — and your stakeholders — will thank you.

Conclusion

A project schedule is only as accurate as the calendar behind it. When holidays aren’t accounted for, every task duration is a guess — and that guess gets worse the longer the project runs.

Microsoft Project gives you precise control over working time at every level: project-wide, per resource, and per task. The process is straightforward: open Change Working Time, add your holiday dates as exceptions, mark them non-working, and assign the right calendar to the right level of your project.

The setup takes minutes. The payoff shows up every time a deadline is met because your schedule actually reflected the real world.