you are definitely not referring to the fields accurately. You also did not include the close parenthesis on the end of your javascript. I have gotten the following code to work. I even made it round to have two decimals only.

BTW, make sure you are using a field that accepts numbers and percentage signs, such as the Single Line type field. 

$(document).ready(function () {
  function round(val){
   return Math.round(val * 100) / 100;
  }

  function numtot() {
    var num1 = $('.num1 input').val();
    var num2 = $('.num2 input').val();

    var result = num2 - num1;
    result = result / num1;
    result = round(result);

    $('.numtotal input').val( result+'%');
  }

  $('.num1').on('change blur', 'input', numtot);
  $('.num2').on('change blur', 'input', numtot);
})