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

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