What Are Project Calendars?

Project Calendars identify the working days and shifts available for scheduled activities. In PMBOK 8, project calendars are a component of the schedule model and a key input to schedule development. They capture non-working time — holidays, organizational shutdowns, resource vacations — that the schedule must account for. A project may have multiple calendars: one for internal team members, one for external vendors operating on different schedules, and one for equipment or facilities with unique availability constraints. Without accurate project calendars, schedule calculations are fiction — activities will be planned on days when no one is working.

What's Inside This Project Calendars Example

This Project Calendars example covers Project Phoenix — MCG's $72,250 website launch, March 17 to June 13, 2025. The spreadsheet contains three calendar tabs:

• MCG Internal Team Calendar: Standard Monday–Friday work week, 8-hour days. Non-working days: Memorial Day (May 26), MCG internal planning day (April 25). Includes each team member's pre-approved vacation: the lead developer (3 days, Week 9) and UX designer (2 days, Week 5).
• BrightFrame Vendor Calendar: Monday–Friday, 9-hour days. Non-working: BrightFrame all-hands summit (April 14–15). This two-day blackout was the reason Alex scheduled the design approval milestone for April 11, not April 14.
• Staging Environment Calendar: The staging server had a scheduled maintenance window every Sunday 10pm–2am, and one planned 4-hour maintenance on April 30. Critical deployments were never scheduled within 6 hours of these windows.

How Alex Morgan Used These Project Calendars

Alex Morgan loaded all three calendars into the project scheduling tool before building the schedule network. This meant every calculated end date already accounted for non-working days — the schedule was realistic from the start rather than optimistic.

Three calendar-related decisions prevented issues during execution:

• BrightFrame summit (April 14–15): By loading the vendor calendar before scheduling, Alex placed the design approval milestone on April 11 with a 3-day buffer before the summit. When the approval meeting ran 30 minutes long on April 11 and minor revisions were needed, the team had until April 13 close-of-business to submit final approval — still clearing the summit blackout.
• Lead developer vacation (Week 9): The lead developer's 3-day absence in Week 9 was on the calendar from Day 1. Alex scheduled non-development tasks (documentation, UAT coordination) for those three days, protecting the critical path.
• Memorial Day: The schedule showed that Memorial Day fell in the middle of the UAT sprint. Alex extended the UAT window by one day to compensate, which prevented the UAT from being artificially compressed.

ISS-007 (Riley Park's sign-off delay in Week 12) was partially anticipated by the calendar: Riley Park's travel dates were not captured in the project calendar because they were confirmed after initial planning. Alex updated the calendar in Week 11 when informed of the travel and flagged the sign-off milestone as at-risk — enabling the async review workaround before it became a crisis.

Download and Customize

This Project Calendars example is available as a free download. Use it as a reference to build your own project calendars, or start with the blank template and populate it for your team and vendor schedule.

• Download the Project Calendars Template — PMBOK 8 (blank, ready to use)
• Read the article: Project Calendars in PMBOK 8 — Guide and Best Practices

Project Calendars Example: Key Takeaways

Project Calendars are one of the least glamorous project management artifacts and one of the most consequential. Every hour spent maintaining accurate calendars at the start of Project Phoenix saved multiple hours of schedule recovery later. The BrightFrame summit example is definitive: a two-day vendor blackout that was loaded into the calendar before schedule development caused zero problems. The same blackout, discovered in Week 4, would have triggered a critical-path delay. The lesson is simple: collect non-working time information from every resource and vendor during planning, load it into the schedule tool before building the network, and update it immediately when new information arrives.

Want to go deeper? The PMBOK Guide 8th Edition is the definitive reference for modern project management. Get your copy and use it alongside these examples to build a solid, practical understanding of every performance domain.