all of which has got nothing to do with the question set by the OP!! who
wanted the last Sunday and not the first Monday!!

"Mike H" wrote:

or

=A1-DAY(A1)+CHOOSE(WEEKDAY(A1-DAY(A1)),1,7,6,5,4,3,2)

"Dale" wrote:

This is probably a very basic question so I apologise first, how would I
calculate the last sunday of a given month? Once I have that date, I need
the following Friday......

Thanks