You need event delegation for change event.try this:
$( "#calculator-wrapper" ).load( "mysite.com/new2/kalkulator/index.php", function(data) {
$(document).on("change",'#calculator',function(){
var formData = $(this).serialize();
$( "#calculator-wrapper" ).load("mysite.com/new2/kalkulator/index.php?"+formData+'&sub=Sz%C3%A1mol');
});});