Date Calculations

#1

Simple issue - I’m calculating performance deadlines from a set date. The formula I’m using is a sum:
sum([Arr Date]-120). I am getting the results I want, but it’s also throwing an error. What am I missing?

#2

OK, I solved part 1 This gives me the correct result without errors:

RelativeDate([Arr Date],-4)

However, I’m now trying to format this to show red when it’s past due, and it is missing the date by several weeks.

#3

Now I’ve solved this too:

[1st Mailing] <= (Today() - 31)

though I am not sure I understand why.