I have built a pivot table that returns a count for both the actual and
planned number of courses completed during a given month. However, now want
to create a calculated field that retruns the difference between the count of
actual and count of planned completions. However as the original data on
which the numbers of completions are counted is in date format I can only get
the pivot table to return a calcualtion of the difference between the dates.

In short what I'm trying to get is

Calculated field= count ('actual complettions') - count ('planned
completions')

rather than Calculated field = 'actual completions' - 'planned completions'