javascript - Age calculation

Question

Having 2 javascript Dates,

first is birthdate and second is a date to calculate age from that date.

What should be the best way to do this.

Answer 1

function calculateAge (birthDate, otherDate) {
    birthDate = new Date(birthDate);
    otherDate = new Date(otherDate);

    var years = (otherDate.getFullYear() - birthDate.getFullYear());

    if (otherDate.getMonth() < birthDate.getMonth() || 
        otherDate.getMonth() == birthDate.getMonth() && otherDate.getDate() < birthDate.getDate()) {
        years--;
    }

    return years;
}

Example:

var age = calculateAge("02/24/1991", "02/24/2010"); // Format: MM/DD/YYYY

Answer 2

Here is a way:

function getAge(d1, d2){
    d2 = d2 || new Date();
    var diff = d2.getTime() - d1.getTime();
    return Math.floor(diff / (1000 * 60 * 60 * 24 * 365.25));
}
console.log( getAge(new Date(1978, 10, 3)) );

Be careful with the month. Javascript counts them from 0.
1978, 10, 3 means the November 3th, 1978

Answer 3

function getAge(dateString) {
  var now = new Date();
  var today = new Date(now.getYear(),now.getMonth(),now.getDate());

  var yearNow = now.getYear();
  var monthNow = now.getMonth();
  var dateNow = now.getDate();

  var dob = new Date(dateString.substring(6,10),
                     dateString.substring(0,2)-1,                   
                     dateString.substring(3,5)                  
                     );

  var yearDob = dob.getYear();
  var monthDob = dob.getMonth();
  var dateDob = dob.getDate();
  var age = {};
  var ageString = "";
  var yearString = "";
  var monthString = "";
  var dayString = "";


  yearAge = yearNow - yearDob;

  if (monthNow >= monthDob)
    var monthAge = monthNow - monthDob;
  else {
    yearAge--;
    var monthAge = 12 + monthNow -monthDob;
  }

  if (dateNow >= dateDob)
    var dateAge = dateNow - dateDob;
  else {
    monthAge--;
    var dateAge = 31 + dateNow - dateDob;

    if (monthAge < 0) {
      monthAge = 11;
      yearAge--;
    }
  }

  age = {
      years: yearAge,
      months: monthAge,
      days: dateAge
      };

  if ( age.years > 1 ) yearString = " years";
  else yearString = " year";
  if ( age.months> 1 ) monthString = " months";
  else monthString = " month";
  if ( age.days > 1 ) dayString = " days";
  else dayString = " day";


  if ( (age.years > 0) && (age.months > 0) && (age.days > 0) )
    ageString = age.years + yearString + ", " + age.months + monthString + ", and " + age.days + dayString + " old.";
  else if ( (age.years == 0) && (age.months == 0) && (age.days > 0) )
    ageString = "Only " + age.days + dayString + " old!";
  else if ( (age.years > 0) && (age.months == 0) && (age.days == 0) )
    ageString = age.years + yearString + " old. Happy Birthday!!";
  else if ( (age.years > 0) && (age.months > 0) && (age.days == 0) )
    ageString = age.years + yearString + " and " + age.months + monthString + " old.";
  else if ( (age.years == 0) && (age.months > 0) && (age.days > 0) )
    ageString = age.months + monthString + " and " + age.days + dayString + " old.";
  else if ( (age.years > 0) && (age.months == 0) && (age.days > 0) )
    ageString = age.years + yearString + " and " + age.days + dayString + " old.";
  else if ( (age.years == 0) && (age.months > 0) && (age.days == 0) )
    ageString = age.months + monthString + " old.";
  else ageString = "Oops! Could not calculate age!";

  return ageString;
}

// A bit of jQuery to call the getAge() function and update the page...
$(document).ready(function() {
  $("#submitDate").click(function(e) {
    e.preventDefault();

    $("#age").html(getAge($("input#date").val()));

  });
});

and HTML IS

Date (MM/DD/YYYY): Calculate Age

Age: 7 years, 1 month, and 15 days old.

Answer 4

Convert the date to milliseconds since the epoch using getTime(), then subtract the values and convert the result back to years:

const MS_PER_YEAR = 1000 * 60 * 60 * 24 * 365.2425;
var years = Math.floor((dateNow.getTime() - dateThen.getTime()) / MS_PER_YEARS);

Answer 5

Here is one example using moment.js library which is very common now days. Just adding this answer in many of other answers.

var banner = $("#banner-message")
var button = $("button")

// handle click and add class
button.on("click", function(){
  var inputValue = $("#txtInput").val();
  var age = parseInt(moment().diff(inputValue,'years',true));
  
$("#spantext").html(age + ' years.');
  
})

body {
  background: #20262E;
  padding: 20px;
  font-family: Helvetica;
}

#banner-message {
  background: #fff;
  border-radius: 4px;
  padding: 20px;
  
  text-align: center;
  transition: all 0.2s;
  margin: 0 auto;
  width: 300px;
}

button {
  background: #0084ff;
  border: none;
  border-radius: 5px;
  padding: 8px 14px;
  font-size: 15px;
  color: #fff;
}

#banner-message.alt {
  background: #0084ff;
  color: #fff;
  margin-top: 40px;
  width: 200px;
}

#banner-message.alt button {
  background: #fff;
  color: #000;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.24.0/moment.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>


<div id="banner-message">
  <p>Enter Date: <input type='text' id='txtInput' value='1981-12-25' /></p>
  <label>Age is : </label><span id='spantext'></span> <br/>
  <p><button>Calculate Age</button></p>
</div>

Answer 6

The best way would probably be to convert the date into a timestamp, probably using parse() if the date is a string. Then simply subtracting the numbers and converting the new number back to a date using new Date(milliseconds)

This might not be too accurate for dates before the 1/1/1970 though, so the alternative method of subtracting days, months, etc... separately would be more suitable.

Answer 7

var birth = new Date('07/11/2003');
var check = new Date();

var milliDay = 1000 * 60 * 60 * 24; // a day in milliseconds;


var ageInDays = (check - birth) / milliDay;

var ageInYears =  Math.floor(ageInDays / 365 );

example http://www.jsfiddle.net/gaby/XDKa3/1/

Answer 8

If you are in an huge Javascript project, you maybe [use|need to use] a framework...

With Mootools More, you have a Date Type with a diff method and a timeDiff method that can fit to your needs.

It even provide localisation !

Answer 9

I've modified Mic's response to allow for today being the user's birthday. The difference is the date you're checking the age of should be set to midnight of that day and/or the current date should be set to 23:59:59. An example would be to see if the user is 18 today, this will return 18.

function getAge(d1){
    var now = new Date();
    var d2 = new Date(now.getFullYear(), now.getMonth(), now.getDate(), 23, 59, 59);
    var diff = d2.getTime() - d1.getTime();
    return Math.floor(diff / (1000 * 60 * 60 * 24 * 365.25));
}
console.log(getAge(new Date(1992, 10, 17, 0, 0, 0)));

Answer 10

This handle leap year use case also:

const getAgeFromBirthDate = (year, month, day) => {
   const date = new Date();
   date.setFullYear(date.getFullYear() - year);
   date.setMonth(date.getMonth() - month);
   //date.setDate(date.getDate() - day);
   return date;
};

console.log( getAgeFromBirthDate(1994, 07, 19).getFullYear() );

Answer 11

A simple way to do this is using moment.js.

We have two dates, the birth date (birthDate) and the other date used to calculate age from (specificDate). You can avoid this parameter and get the current age.

moment(specificDate).diff(moment(birthDate), 'years');

Hope it helps you!

Answer 12

function getAge(dateOfBirth, tillDate) {
    var dob = new Date(dateOfBirth);
    var endDt = new Date(tillDate) || new Date();
    return new Date(endDt.getTime() - dob.getTime()).getUTCFullYear() - 1970;
}

Example: console.log(getAge('1/1/2000', '1/1/2016')); // Format: MM/DD/YYYY

Answer 13

Get age calculating by current year

calculateExp(birthDate) {
    birthDate = new Date(birthDate);
    var now = new Date();
    otherDate = new Date(now.getFullYear(),now.getMonth(),now.getDate());
    var years = (otherDate.getFullYear() - birthDate.getFullYear() );


    if (otherDate.getMonth() < birthDate.getMonth() || otherDate.getMonth() == birthDate.getMonth() && otherDate.getDate() < birthDate.getDate()) {
        years--;
    }

    return years;
}

Answer 14

This script helps you do the following;

• Calculate age using start date and end date
• Determine if year is leap year or not
• Calculate the number of days in a month
• Determine if it is an end month
• Calculate the number of weekends between two dates
• Determine the next day from a given date

Here is the script; https://github.com/amoschihi/age-calculator

determineAge('2001-01-24','2022-04-03');
  // output: 21 Years, 2 Months and 9 Days