Over the past 19 years, when I delivered training courses in Microsoft Project (versions 1998, 2000, 2002) and education in Microsoft Project (versions 2007, 2010, 2013, 2016) one of the questions I was often asked was “How do you customise the calendars?”

On the training courses, nothing was so sure to add more errors to the delegates files than messing with the calendars – difficult to use, not intuitive to change, and difficult to find the exceptions. So difficult in fact that it was removed from the introductory training course!

The operation of the calendar has changed over the years, but still needs some thought.

A Standard 8 hour day and 40 hour week

The default in Microsoft Project is an 8 hour day and 40 hour week. Few UK companies work to the standard default pattern of 8 hours a day (8:00 – 12:00, and 13:00 – 17:00). Hence the frequent request to set up 7:30 start times, 4:30 finish times, or 13:00 finish times on Fridays to model the more usual (in the UK) 37, 37.5 or 38 hour week.

Default Calendar Settings

Default Calendar Settings

But please stop, and think before going to the effort of changing the calendars.

How Accurate are your Estimates?

The difference between a 37 hour week and a 40 hour week is 3 hours – or about 8%. Are your duration, work and cost estimates really within 8% for your project? Is a difference of 8% in the calendars really going to make a difference?

Work and Duration

Do your team give you estimates of both work content (effort) and duration? If you are just modelling duration, then why worry about the missing work hours?

Work and Duration are different. 20 hours of work, may take a week to complete. If your team member has just supplied you with the duration (1 week), then it really doesn’t matter if your Microsoft Project Calendars are set up for 37 or 40 hour weeks.

Even if you have correctly entered the work as 20 hours, and the duration as 1 week, the added accuracy of a 37 hour calendar will make very little difference to the project plan. When the team member suggested 20 hours (with some thought) was the 1 week duration just a throw-away remark?

Project Plans are Built from Estimates.

Good estimates lead to good project plans, and good project plans indicate good project managers. However, you will not be entering every single task into Project. The old motto is Keep it Simple Stupid – KISS. Editing the calendars adds complexity and can become a source of errors.

Change the Correct Calendar

There are actually three different calendar types in Microsoft Project;

  • Project Calendars – use these to set the default for the entire project
  • Resource Calendars – use these to set up specific resource calendars for shift workers
  • Task Calendars – use these for tasks that have to be performed at specific times

So perhaps a resource calendar is required rather than an edit to the project calendar?

So When Can You Edit the Calendar?

Having recommended no changes at all, I will write a future blog on how you really do edit the Microsoft Project calendar. However, a good use is to enter non-working days – the public holidays – or the complete work shutdown periods. However, people could still be asked to work in these periods.

Calendars. Think of reasons for NOT editing the calendar first, and only edit them when it is really required.


Posted On: 2nd January 2018

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