Calculate Age From Birthday

This JavaScript will perform age verification based on the date of birth entered in an open-text field. The qualifying age can be set in the script (18 years old, 21 years old, etc.) and if the user is not old enough, they will be disqualified. If they are old enough, the script does nothing and allows them to move forward through the survey. You can also customize the disqualification message as well. If you prefer Custom Scripting to JavaScript, check out our tutorial on Age Verification by Birth Date in Custom Scripting. 

Check it out in a survey:

http://www.surveygizmo.com/s3/2033346/Working-Example-Calculate-Age-from-Birth-Date

OR

Add a survey with this setup to your account!

This script uses the following question types or actions:

• Textbox Question (for Birth Date)
• Textbox Question (for Age) Or Hidden Value
• Javascript Action

Setup

First build out your survey page with your birth date textbox and age textbox or hidden value. Next click Add New Action > JavaScript. Paste the below JavaScript. 

$(document).ready(function(){
if($('body').attr('id') != 'app') {

var textbox = $('#sgE-2033346-1-2-element');  //dob box
$tgtbox = $("#sgE-2033346-1-4-element"); //age box
$minage = 18;  //minimum age
$errortxt = 'You must be at least ' + $minage + ' years old to continue';
  
  
textbox.change(function(){
console.log($(this).val());
var birth = $(this).val();

function getAge(birth) {

var d = new Date();
var n = d.getTime();
console.log(n);

var c = Date.parse(birth);
console.log(c);

var a = (d - c) /(1000*60*60*24*365);
var result=Math.round(a*100)/100;
console.log(result);

   $tgtbox.val(Math.floor(result));
   //alert(result);
}
getAge(birth);
});
}

  
//submit validation  
$('.sg-survey-form').submit(function(e){
  
  if($tgtbox.val() < $minage) {
    //alert($tgtbox.val());
    //alert($minage);
    
    $('.sg-error-message').text($errortxt).fadeIn('slow');
    e.preventDefault();
    
  }
});  //end submit validation
});

Required Modifications

The highlighted blue elements above will need to be changed to match your survey. 

The element var textbox = $('#sgE-2033346-1-2-element'); will need to be updated with the birth date textbox element ID.

The element $tgtbox = $("#sgE-2033346-1-4-element"); will need to be updated with the element ID of the hidden value or textbox associated with the respondent's age. 

$minage = 18;  //Minimum Age-This is the age limit you would like to set. Any response received with an age limit below this age (in years) will be disqualified. For example, if you do not want anyone under the age of 30 to fill out your survey, you'd want to change the number 18 to 30. 

To learn how to find your individual element IDs check out our awesome tutorial on How to Find Element IDs.