How can I calculate the number of years between two dates?

Question

I want to get the number of years between two dates. I can get the number of days between these two days, but if I divide it by 365 the result is incorrect because some years have 366 days.

This is my code to get date difference:

var birthday = value;//format 01/02/1900
var dateParts = birthday.split("/");

var checkindate = new Date(dateParts[2], dateParts[0] - 1, dateParts[1]);   
var now = new Date();
var difference = now - checkindate;
var days = difference / (1000*60*60*24);

var thisyear = new Date().getFullYear();
var birthyear = dateParts[2];

    var number_of_long_years = 0;
for(var y=birthyear; y <= thisyear; y++){   

    if( (y % 4 == 0 && y % 100 == 0) || y % 400 == 0 ) {

                    number_of_long_years++;             
    }
}   

The day count works perfectly. I am trying to do add the additional days when it is a 366-day year, and I'm doing something like this:

var years = ((days)*(thisyear-birthyear))
            /((number_of_long_years*366) + ((thisyear-birthyear-number_of_long_years)*365) );

I'm getting the year count. Is this correct, or is there a better way to do this?

Answer 1

Sleek foundation javascript function.

 function calculateAge(birthday) { // birthday is a date
   var ageDifMs = Date.now() - birthday;
   var ageDate = new Date(ageDifMs); // miliseconds from epoch
   return Math.abs(ageDate.getUTCFullYear() - 1970);
 }

Answer 2

Probably not the answer you're looking for, but at 2.6kb, I would not try to reinvent the wheel and I'd use something like moment.js. Does not have any dependencies.

The diff method is probably what you want: http://momentjs.com/docs/#/displaying/difference/

Answer 3

Using pure javascript Date(), we can calculate the numbers of years like below

document.getElementById('getYearsBtn').addEventListener('click', function () {
  var enteredDate = document.getElementById('sampleDate').value;
  // Below one is the single line logic to calculate the no. of years...
  var years = new Date(new Date() - new Date(enteredDate)).getFullYear() - 1970;
  console.log(years);
});

<input type="text" id="sampleDate" value="1980/01/01">
<div>Format: yyyy-mm-dd or yyyy/mm/dd</div><br>
<button id="getYearsBtn">Calculate Years</button>

Answer 4

No for-each loop, no extra jQuery plugin needed... Just call the below function.. Got from Difference between two dates in years

        function dateDiffInYears(dateold, datenew) {
            var ynew = datenew.getFullYear();
            var mnew = datenew.getMonth();
            var dnew = datenew.getDate();
            var yold = dateold.getFullYear();
            var mold = dateold.getMonth();
            var dold = dateold.getDate();
            var diff = ynew - yold;
            if (mold > mnew) diff--;
            else {
                if (mold == mnew) {
                    if (dold > dnew) diff--;
                }
            }
            return diff;
        }

Answer 5

I use the following for age calculation.

I named it gregorianAge() because this calculation gives exactly how we denote age using Gregorian calendar. i.e. Not counting the end year if month and day is before the month and day of the birth year.

/**
 * Calculates human age in years given a birth day. Optionally ageAtDate
 * can be provided to calculate age at a specific date
 *
 * @param string|Date Object birthDate
 * @param string|Date Object ageAtDate optional
 * @returns integer Age between birthday and a given date or today
 */
gregorianAge = function(birthDate, ageAtDate) {
  // convert birthDate to date object if already not
  if (Object.prototype.toString.call(birthDate) !== '[object Date]')
    birthDate = new Date(birthDate);

  // use today's date if ageAtDate is not provided
  if (typeof ageAtDate == "undefined")
    ageAtDate = new Date();

  // convert ageAtDate to date object if already not
  else if (Object.prototype.toString.call(ageAtDate) !== '[object Date]')
    ageAtDate = new Date(ageAtDate);

  // if conversion to date object fails return null
  if (ageAtDate == null || birthDate == null)
    return null;


  var _m = ageAtDate.getMonth() - birthDate.getMonth();

  // answer: ageAt year minus birth year less one (1) if month and day of
  // ageAt year is before month and day of birth year
  return (ageAtDate.getFullYear()) - birthDate.getFullYear()
    - ((_m < 0 || (_m === 0 && ageAtDate.getDate() < birthDate.getDate()))?1:0)
}

<input type="text" id="birthDate" value="12 February 1982">
<div style="font-size: small; color: grey">Enter a date in an acceptable format e.g. 10 Dec 2001</div><br>
<button onClick='js:alert(gregorianAge(document.getElementById("birthDate").value))'>What's my age?</button>

Answer 6

Little out of date but here is a function you can use!

function calculateAge(birthMonth, birthDay, birthYear) {
    var currentDate = new Date();
    var currentYear = currentDate.getFullYear();
    var currentMonth = currentDate.getMonth();
    var currentDay = currentDate.getDate(); 
    var calculatedAge = currentYear - birthYear;

    if (currentMonth < birthMonth - 1) {
        calculatedAge--;
    }
    if (birthMonth - 1 == currentMonth && currentDay < birthDay) {
        calculatedAge--;
    }
    return calculatedAge;
}

var age = calculateAge(12, 8, 1993);
alert(age);

Answer 7

You can get the exact age using timesstamp:

const getAge = (dateOfBirth, dateToCalculate = new Date()) => {
    const dob = new Date(dateOfBirth).getTime();
    const dateToCompare = new Date(dateToCalculate).getTime();
    const age = (dateToCompare - dob) / (365 * 24 * 60 * 60 * 1000);
    return Math.floor(age);
};

Answer 8

let currentTime = new Date().getTime();
let birthDateTime= new Date(birthDate).getTime();
let difference = (currentTime - birthDateTime)
var ageInYears=difference/(1000*60*60*24*365)

Answer 9

Yep, moment.js is pretty good for this:

var moment = require('moment');
var startDate = new Date();
var endDate = new Date();
endDate.setDate(endDate.getFullYear() + 5); // Add 5 years to second date
console.log(moment.duration(endDate - startDate).years()); // This should returns 5

Answer 10

function getYearDiff(startDate, endDate) {
    let yearDiff = endDate.getFullYear() - startDate.getFullYear();
    if (startDate.getMonth() > endDate.getMonth()) {
        yearDiff--;
    } else if (startDate.getMonth() === endDate.getMonth()) {
        if (startDate.getDate() > endDate.getDate()) {
            yearDiff--;
        } else if (startDate.getDate() === endDate.getDate()) {
            if (startDate.getHours() > endDate.getHours()) {
                yearDiff--;
            } else if (startDate.getHours() === endDate.getHours()) {
                if (startDate.getMinutes() > endDate.getMinutes()) {
                    yearDiff--;
                }
            }
        }
    }
    return yearDiff;
}

alert(getYearDiff(firstDate, secondDate));

Answer 11

getAge(month, day, year) {
    let yearNow = new Date().getFullYear();
    let monthNow = new Date().getMonth() + 1;
    let dayNow = new Date().getDate();
    if (monthNow === month && dayNow < day || monthNow < month) {
      return yearNow - year - 1;
    } else {
      return yearNow - year;
    }
  }

Answer 12

If you are using moment

/**
 * Convert date of birth into age
 * param {string} dateOfBirth - date of birth
 * param {string} dateToCalculate  -  date to compare
 * returns {number} - age
 */
function getAge(dateOfBirth, dateToCalculate) {
    const dob = moment(dateOfBirth);
    return moment(dateToCalculate).diff(dob, 'years');
};

Answer 13

getYears(date1, date2) {
let years = new Date(date1).getFullYear() - new Date(date2).getFullYear();
let month = new Date(date1).getMonth() - new Date(date2).getMonth();
let dateDiff = new Date(date1).getDay() - new Date(date2).getDay();
if (dateDiff < 0) {
    month -= 1;
}
if (month < 0) {
    years -= 1;
}
return years;
}

Answer 14

for(var y=birthyear; y <= thisyear; y++){ 

if( (y % 4 == 0 && y % 100 == 0) || y % 400 == 0 ) { 
 days = days-366;
 number_of_long_years++; 
} else {
    days=days-365;
}

year++;

}

---

can you try this way??

Answer 15

Date calculation work via the Julian day number. You have to take the first of January of the two years. Then you convert the Gregorian dates into Julian day numbers and after that you take just the difference.

Answer 16

Maybe my function can explain better how to do this in a simple way without loop, calculations and/or libs

function checkYearsDifference(birthDayDate){
    var todayDate = new Date();
    var thisMonth = todayDate.getMonth();
    var thisYear = todayDate.getFullYear();
    var thisDay = todayDate.getDate();
    var monthBirthday = birthDayDate.getMonth(); 
    var yearBirthday = birthDayDate.getFullYear();
    var dayBirthday = birthDayDate.getDate();
    //first just make the difference between years
    var yearDifference = thisYear - yearBirthday;
    //then check months
    if (thisMonth == monthBirthday){
      //if months are the same then check days
      if (thisDay<dayBirthday){
        //if today day is before birthday day
        //then I have to remove 1 year
        //(no birthday yet)
        yearDifference = yearDifference -1;
      }
      //if not no action because year difference is ok
    }
    else {
      if (thisMonth < monthBirthday) {
        //if actual month is before birthday one
        //then I have to remove 1 year
        yearDifference = yearDifference -1;
      }
      //if not no action because year difference is ok
    }
    return yearDifference;
  }

Answer 17

Bro, moment.js is awesome for this: The diff method is what you want: http://momentjs.com/docs/#/displaying/difference/

The below function return array of years from the year to the current year.

const getYears = (from = 2017) => {
  const diff = moment(new Date()).diff(new Date(`01/01/${from}`), 'years') ;
  return [...Array(diff >= 0 ? diff + 1 : 0).keys()].map((num) => {
    return from + num;
  });
}

console.log(getYears(2016));

<script src="https://momentjs.com/downloads/moment.js"></script>

Answer 18

function dateDiffYearsOnly( dateNew,dateOld) {
   function date2ymd(d){ w=new Date(d);return [w.getFullYear(),w.getMonth(),w.getDate()]}
   function ymd2N(y){return (((y[0]<<4)+y[1])<<5)+y[2]} // or 60 and 60 // or 13 and 32 // or 25 and 40 //// with ...
   function date2N(d){ return ymd2N(date2ymd(d))}

   return  (date2N(dateNew)-date2N(dateOld))>>9
}

test:

dateDiffYearsOnly(Date.now(),new Date(Date.now()-7*366*24*3600*1000));
dateDiffYearsOnly(Date.now(),new Date(Date.now()-7*365*24*3600*1000))

Answer 19

This one Help you...

     $("[id$=btnSubmit]").click(function () {
        debugger
        var SDate = $("[id$=txtStartDate]").val().split('-');
        var Smonth = SDate[0];
        var Sday = SDate[1];
        var Syear = SDate[2];
        // alert(Syear); alert(Sday); alert(Smonth);
        var EDate = $("[id$=txtEndDate]").val().split('-');
        var Emonth = EDate[0];
        var Eday = EDate[1];
        var Eyear = EDate[2];
        var y = parseInt(Eyear) - parseInt(Syear);
        var m, d;
        if ((parseInt(Emonth) - parseInt(Smonth)) > 0) {
            m = parseInt(Emonth) - parseInt(Smonth);
        }
        else {
            m = parseInt(Emonth) + 12 - parseInt(Smonth);
            y = y - 1;
        }
        if ((parseInt(Eday) - parseInt(Sday)) > 0) {
            d = parseInt(Eday) - parseInt(Sday);
        }
        else {
            d = parseInt(Eday) + 30 - parseInt(Sday);
            m = m - 1;
        }
        // alert(y + " " + m + " " + d);
        $("[id$=lblAge]").text("your age is " + y + "years  " + m + "month  " + d + "days");
        return false;
    });

Answer 20

if someone needs for interest calculation year in float format

function floatYearDiff(olddate, newdate) {
  var new_y = newdate.getFullYear();
  var old_y = olddate.getFullYear();
  var diff_y = new_y - old_y;
  var start_year = new Date(olddate);
  var end_year = new Date(olddate);
  start_year.setFullYear(new_y);
  end_year.setFullYear(new_y+1);
  if (start_year > newdate) {
    start_year.setFullYear(new_y-1);
    end_year.setFullYear(new_y);
    diff_y--;
  }
  var diff = diff_y + (newdate - start_year)/(end_year - start_year);
  return diff;
}