Calculate age given the birth date in the format Y

Question

How can I calculate an age in years, given a birth date of format YYYYMMDD? Is it possible using the Date() function?

I am looking for a better solution than the one I am using now:

var dob = '19800810';
var year = Number(dob.substr(0, 4));
var month = Number(dob.substr(4, 2)) - 1;
var day = Number(dob.substr(6, 2));
var today = new Date();
var age = today.getFullYear() - year;
if (today.getMonth() < month || (today.getMonth() == month && today.getDate() < day)) {
  age--;
}
alert(age);

Answer 1

here is a simple way of calculating age:

//dob date dd/mm/yy 
var d = 01/01/1990


//today
//date today string format 
var today = new Date(); // i.e wed 04 may 2016 15:12:09 GMT
//todays year
var todayYear = today.getFullYear();
// today month
var todayMonth = today.getMonth();
//today date
var todayDate = today.getDate();

//dob
//dob parsed as date format   
var dob = new Date(d);
// dob year
var dobYear = dob.getFullYear();
// dob month
var dobMonth = dob.getMonth();
//dob date
var dobDate = dob.getDate();

var yearsDiff = todayYear - dobYear ;
var age;

if ( todayMonth < dobMonth ) 
 { 
  age = yearsDiff - 1; 
 }
else if ( todayMonth > dobMonth ) 
 {
  age = yearsDiff ; 
 }

else //if today month = dob month
 { if ( todayDate < dobDate ) 
  {
   age = yearsDiff - 1;
  }
    else 
    {
     age = yearsDiff;
    }
 }

Answer 2

var now = DateTime.Now;
var age = DateTime.Now.Year - dob.Year;
if (now.Month < dob.Month || now.Month == dob.Month && now.Day < dob.Day) age--;

Answer 3

With momentjs "fromNow" method, This allows you to work with formatted date, ie: 03/15/1968

var dob = document.getElementByID("dob"); var age = moment(dob.value).fromNow(true).replace(" years", "");

//fromNow(true) => suffix "ago" is not displayed //but we still have to get rid of "years";

As a prototype version

String.prototype.getAge = function() {
return moment(this.valueOf()).fromNow(true).replace(" years", "");

}

Answer 4

Alternate solution, because why not:

function calculateAgeInYears (date) {
    var now = new Date();
    var current_year = now.getFullYear();
    var year_diff = current_year - date.getFullYear();
    var birthday_this_year = new Date(current_year, date.getMonth(), date.getDate());
    var has_had_birthday_this_year = (now >= birthday_this_year);

    return has_had_birthday_this_year
        ? year_diff
        : year_diff - 1;
}

Answer 5

I just had to write this function for myself - the accepted answer is fairly good but IMO could use some cleanup. This takes a unix timestamp for dob because that was my requirement but could be quickly adapted to use a string:

var getAge = function(dob) {
    var measureDays = function(dateObj) {
            return 31*dateObj.getMonth()+dateObj.getDate();
        },
        d = new Date(dob*1000),
        now = new Date();

    return now.getFullYear() - d.getFullYear() - (measureDays(now) < measureDays(d));
}

Notice I've used a flat value of 31 in my measureDays function. All the calculation cares about is that the "day-of-year" be a monotonically increasing measure of the timestamp.

If using a javascript timestamp or string, obviously you'll want to remove the factor of 1000.

Answer 6

Here's my solution, just pass in a parseable date:

function getAge(birth) {
  ageMS = Date.parse(Date()) - Date.parse(birth);
  age = new Date();
  age.setTime(ageMS);
  ageYear = age.getFullYear() - 1970;

  return ageYear;

  // ageMonth = age.getMonth(); // Accurate calculation of the month part of the age
  // ageDay = age.getDate();    // Approximate calculation of the day part of the age
}