Why Don’t My Finish Dates Correspond to My Activity Durations in P6?

So you schedule your project and things look great and you’re even finishing sooner than you thought!  Unfortunately, upon closer examination, you realize that your durations don’t seem to be matching up with your finish dates, so it looks like you are finishing each activity earlier than you should be.  What’s going on?   In this scenario, you are likely displaying your activity durations in days.  We all know that a “day” on one assigned activity calendar may translate to 8 hours, while on another calendar it may be 10 hours.  And we’re all ecstatic that beginning with P6 v. 7, Oracle Primavera also realized this likely scenario and provided an option in the Admin Preferences that allows you to “Use assigned calendar to specify the number of work hours for each time period” by simply checking a box on the Time Periods tab.  Below are a couple of noteworthy reminders that will likely shed light on why your durations and dates may not jive when using this option:

P6 always calculates in hours. You can view in days, but in the background it calculates in hours.  If your dates look funky, select to show time on the Dates tab in your User Preferences (My Preferences – P6 R8) and you’ll see why.

Expect finish dates to change if you change a calendar’s time periods mid-stream. Be aware that if you change the hours per day on the calendar after you have noted the “daily” durations in the duration column, behind the scenes the durations are automatically going to recalculate in hours in the background. So, if you increase the hours per day on the calendar, depending on the length of the duration, the days may look the same on screen, but the activity will end on an earlier calendar date based off of the hours calculation.  If you decrease your hours per day, again, depending on the length of the duration, you’re likely to see your activity finish dates push out into the future.

Confirm time periods when creating new calendars. When creating new calendars, time periods will be copied over from the template calendar you used. So make sure to check the time periods for the new calendar, preferably before they are assigned to activities.