Calculate number of months between a Start Date and End Date

1. Number of Months Start Date Month to the end of the year
2. Number of Months from January to the End Date Month
3. Number of Whole years between the Start Date and End Date

var date SD=[Start Date];
var date ED=[End Date];

//Number of Months in Start Year
var number sm = 13 - Month($sd);

//Number of Months in End Year
var number em = Month($ed);

//Number of Months between Start and End
var number wm = (Year($ED)-Year($SD)-1)*12;

//Total
$sm + $em + $wm​

var date SD=[Start Date];
var date ED=[End Date];

// start off with 12 times the number of fully completed years
(Year($ED)-Year($SD)-1)*12 

//add 12 months if the last year was fully completed
+If(Month($ED)>=Month($SD),12,0)

// add the number of months between the month numbers
+If((Month($ED)>=Month($SD)),Month($ED)-Month($SD),12+Month($ED)-Month($SD))

// but if the day did not catch up to the start date's day number, then subtract 1
-If(Day($ED)<Day($SD),1,0) ​