Set Age from DOB Question

Ehtesham Mirza

Modified on: Wed, 7 Oct, 2026 at 11:52 AM

You can use JavaScript to set the numeric age in a hidden question after you have asked the Date of Birth question.

This code below relies on you piping through the answer from the previous question:

function pageReady() {  

    // Get DOB string from hidden cRef element  

    var dobStr = $(".cRef").eq(0).text().trim();
  

    if (!dobStr) return;
  // Expecting dd/mm/yyyy  

    var parts = dobStr.split("/");  

    if (parts.length !== 3) return;
      

    var day   = parseInt(parts[0], 10);  

    var month = parseInt(parts[1], 10) - 1; 

    // JS months are 0-based  

    var year  = parseInt(parts[2], 10);

    if (isNaN(day) || isNaN(month) || isNaN(year)) return;
  

    var dob   = new Date(year, month, day);  

    var today = new Date();
    var age = today.getFullYear() - dob.getFullYear();

    var monthDiff = today.getMonth() - dob.getMonth();

    var dayDiff = today.getDate() - dob.getDate();
  

    // Adjust if birthday hasn't occurred yet this year

    if (monthDiff < 0 || (monthDiff === 0 && dayDiff < 0)) {age--;}
    // Safety check  

    if (age < 0 || age > 120) return;

    // DCv2: numeric fields use .numeric-decimal-input, fire 'input' event  

    $(".numeric-decimal-input").eq(0).val(age).trigger("input");
    $(".main-next-button").click();  

    $(".main-back-button").hide();

}