Difference in Months between two dates in JavaScript

Question

How would I work out the difference for two Date() objects in JavaScript, while only return the number of months in the difference?

Any help would be great :)

Answer 1

getMonthDiff(d1, d2) {
    var year1 = dt1.getFullYear();
    var year2 = dt2.getFullYear();
    var month1 = dt1.getMonth();
    var month2 = dt2.getMonth();
    var day1 = dt1.getDate();
    var day2 = dt2.getDate();
    var months = month2 - month1;
    var years = year2 -year1
    days = day2 - day1;
    if (days < 0) {
        months -= 1;
    }
    if (months < 0) {
        months += 12;
    }
    return months + years*!2;
}

Answer 2

function calcualteMonthYr(){
    var fromDate =new Date($('#txtDurationFrom2').val()); //date picker (text fields)
    var toDate = new Date($('#txtDurationTo2').val());

var months=0;
        months = (toDate.getFullYear() - fromDate.getFullYear()) * 12;
        months -= fromDate.getMonth();
        months += toDate.getMonth();
            if (toDate.getDate() < fromDate.getDate()){
                months--;
            }
    $('#txtTimePeriod2').val(months);
}

Answer 3

Number Of Months When Day & Time Doesn't Matter

In this case, I'm not concerned with full months, part months, how long a month is, etc. I just need to know the number of months. A relevant real world case would be where a report is due every month, and I need to know how many reports there should be.

Example:

• January = 1 month
• January - February = 2 months
• November - January = 3 months

This is an elaborated code example to show where the numbers are going.

Let's take 2 timestamps that should result in 4 months

• November 13, 2019's timestamp: 1573621200000
• February 20, 2020's timestamp: 1582261140000

May be slightly different with your timezone / time pulled. The day, minutes, and seconds don't matter and can be included in the timestamp, but we will disregard it with our actual calculation.

Step 1: convert the timestamp to a JavaScript date

let dateRangeStartConverted = new Date(1573621200000);
let dateRangeEndConverted = new Date(1582261140000);

Step 2: get integer values for the months / years

let startingMonth = dateRangeStartConverted.getMonth();
let startingYear = dateRangeStartConverted.getFullYear();
let endingMonth = dateRangeEndConverted.getMonth();
let endingYear = dateRangeEndConverted.getFullYear();

This gives us

• Starting month: 11
• Starting Year: 2019
• Ending month: 2
• Ending Year: 2020

Step 3: Add (12 * (endYear - startYear)) + 1 to the ending month.

• This makes our starting month stay at 11
• This makes our ending month equal 15 2 + (12 * (2020 - 2019)) + 1 = 15

Step 4: Subtract the months

15 - 11 = 4; we get our 4 month result.

29 Month Example Example

November 2019 through March 2022 is 29 months. If you put these into an excel spreadsheet, you will see 29 rows.

• Our starting month is 11
• Our ending month is 40 3 + (12 * (2022-2019)) + 1

40 - 11 = 29

Answer 4

anyVar = (((DisplayTo.getFullYear() * 12) + DisplayTo.getMonth()) - ((DisplayFrom.getFullYear() * 12) + DisplayFrom.getMonth()));

Answer 5

Calculate the difference between two dates include fraction of month (days).

---

var difference = (date2.getDate() - date1.getDate()) / 30 +
    date2.getMonth() - date1.getMonth() +
    (12 * (date2.getFullYear() - date1.getFullYear()));

For example:
date1: 24/09/2015 (24th Sept 2015)
date2: 09/11/2015 (9th Nov 2015)
the difference: 2.5 (months)

Answer 6

The definition of "the number of months in the difference" is subject to a lot of interpretation. :-)

You can get the year, month, and day of month from a JavaScript date object. Depending on what information you're looking for, you can use those to figure out how many months are between two points in time.

For instance, off-the-cuff:

function monthDiff(d1, d2) {
    var months;
    months = (d2.getFullYear() - d1.getFullYear()) * 12;
    months -= d1.getMonth();
    months += d2.getMonth();
    return months <= 0 ? 0 : months;
}

function monthDiff(d1, d2) {
    var months;
    months = (d2.getFullYear() - d1.getFullYear()) * 12;
    months -= d1.getMonth();
    months += d2.getMonth();
    return months <= 0 ? 0 : months;
}

function test(d1, d2) {
    var diff = monthDiff(d1, d2);
    console.log(
        d1.toISOString().substring(0, 10),
        "to",
        d2.toISOString().substring(0, 10),
        ":",
        diff
    );
}

test(
    new Date(2008, 10, 4), // November 4th, 2008
    new Date(2010, 2, 12)  // March 12th, 2010
);
// Result: 16

test(
    new Date(2010, 0, 1),  // January 1st, 2010
    new Date(2010, 2, 12)  // March 12th, 2010
);
// Result: 2

test(
    new Date(2010, 1, 1),  // February 1st, 2010
    new Date(2010, 2, 12)  // March 12th, 2010
);
// Result: 1

(Note that month values in JavaScript start with 0 = January.)

Including fractional months in the above is much more complicated, because three days in a typical February is a larger fraction of that month (~10.714%) than three days in August (~9.677%), and of course even February is a moving target depending on whether it's a leap year.

There are also some date and time libraries available for JavaScript that probably make this sort of thing easier.

---

Note: There used to be a + 1 in the above, here:

months = (d2.getFullYear() - d1.getFullYear()) * 12;
months -= d1.getMonth() + 1;
// −−−−−−−−−−−−−−−−−−−−^^^^
months += d2.getMonth();

That's because originally I said:

...this finds out how many full months lie between two dates, not counting partial months (e.g., excluding the month each date is in).

I've removed it for two reasons:

1. Not counting partial months turns out not to be what many (most?) people coming to the answer want, so I thought I should separate them out.

2. It didn't always work even by that definition. :-D (Sorry.)