Error with this formula where [Bound Date] = $SD:
var date ED= IF(Year([Expiration Date 1])<> Year(Today()), Date(Year(Today()),12,31), [Expiration Date 1]));
(Year($ED)-Year([Bound Date])-1)*12 // start off with 12 times the number of fully completed years
+If(Month($ED)>=Month([Bound Date]),12,0) //add 12 months if the last year was fully completed
+ If((Month($ED)>=Month([Bound Date])),Month($ED)-Month([Bound Date]),12+Month($ED)-Month([Bound Date])) // add the number of months between the month numbers.
-If(Day($ED)<Day([Bound Date]),1,0) // but if the day did not catch up to the start date's day number, then subtract 1.
