Calculate Months from Field Date

Question

Using: Acrobat X Pro in windows. 
I have three fields:
1) Today's Date:___________ [DateToday] -- Automatically filled-in with today's date using script.
2) Date Last Payment Made:__________ [LastPaymentMade1] -- Filled-in by user in mm/dd/yyyy format.
3) Months Since Last Payment:______________ [MoBehind] -- Need to calculate from field 1 - 2).
For #3, how do I custom calculate how many MONTHS it has been (#3) since the date the last payment was made (#2)?
There's a great discussion here on this topic but I cannot figure out how to modify the script for my purposes: http://forums.adobe.com/message/1907993#1907993
This appears to be the closest thing to what I want:
function Floor(fValue) {
return Math.floor(fValue);
function Date2Num(sDate, sFormat) {
var fSecond =1000;
var fMinute = 60 * fSecond;
var fHour = 60 * fMinute;
var fDay = 24 * fHour;
var oDate = util.scand(sFormat, sDate);
var fDate = oDate.valueOf();
var fDate = fDate / fDay;
var fDate = Floor(fDate);
return fDate;
var Start = this.getField("DateToday").value;
var sFormat = "mm/dd/yyyy";
var End = this.getField("LastPaymentMade1").value;
var sFormat = "mm/dd/yyyy";
var eFormat = sFormat;
event.value = Date2Num(End, eFormat) - Date2Num(Start, sFormat);
Here's another one that looks SIMILAR to what i want:
(function () {
    // Get date from field
    var v = getField("DateToday").value;
    if (v) {
        // Convert string to date
        var d = util.scand('mm/dd/yyyy', v);
        // Add number of days in NUMDAYS field
        d.setDate(d.getDate() - +getField("NumDays").value);
        // Set value of this field to the new date
        event.value = util.printd("mm/dd/yyyy", d);
    } else {
        // Blank field if no date entered
        event.value = "";

Answer 1

Since the number of days in a month are not constant across a year I do not think you can use the milliseconds in a day.
I you use the 'getMonth()' and 'getFullYear()' methods for the calculation.
// get the date values
var Start = this.getField("DateToday").value;
var sFormat = "mm/dd/yyyy";
var End = this.getField("LastPaymentMade1").value;
var sFormat = "mm/dd/yyyy";
var eFormat = sFormat;
// convert to date object
var oStart = util.scand(sForamt, Start);
var oEnd = util.scand(eFormat, End);
// get start month
var StartMonth = oStrat.getMonth();
// add start full year as months
StartMonth = StartMonth + (oStart.getFullYear() * 12);
// get end month
var EndMonth = oEnd.getMonth();
// add end full year as months
EndMonth = EndMonth + (oEnd.getFullYear() * 12);
// compute difference in months
var diffMonths = EndMonth - StratMonth;