Previous Month from text field

[zagzebski]

I have an "Effective Date" text field in the following format:

ex.  Effective Date = 20140410  ( April 10 of 2014)

I need to be able to change this to a text field that would represent the previous month (in a YYYYMM format):

20140410  becomes 201403

20140115  becomes 201312

Thanks for any help in advance,

Steve

[Gysbert_Wassenaar · Accepted solution]

date(monthstart( date#([Effective Date], 'YYYYMMDD'),-1),'YYYYMM')

[zagzebski]

Thanks!