Converting Date field to a string field with just the month and day

I've been working (google and the forums) on this problem have not been able to get the complete solution. I hope the forums may be able to help me.

I have a date field in a shape file (EXPIRY_DAT) I would like to use the field calculator to update a text field (DUE_Date) with a new date that is 180 day from EXPIRY_DAT. The part I'm unable to figure out is how to have the final result in DUE_DATE just show the month and day.

example:

EXPIRY_DAT = 10/05/2017

DUE_DATE = November 6 or 11/06

The closest I have come to an answer is:

VBA: FormatDateTime( [EXPIRY_DAT]+180, vblongdate)

or

Python: time.strftime('%m/%d')
I like the python solution, but I don't know how to get it to work on the EXPIRY_DAT field, only the current date.

Thank you for any help you're able to offer me.

Chris