jQuery sum checkbox values

I'd need to calculate sum of all checkboxes and update total based on selection here is html:

<input type="checkbox" id="basic_single" name="basic_single" value="400">
<input type="checkbox" id="basic_double" name="basic_double" value="680">
.
.
.
<input type="text" name="total" value="" size="30" id="total">

here is the script

   $('input:checkbox').change(function ()
     {
      var total = 0;
      var basic_single = parseInt($('#basic_single:checked').val());
      var basic_double = parseInt($('#basic_double:checked').val());

      var total = basic_single + basic_double;

      $("#total").val(total);

    });

if both are checked it works fine, but just one checked returns NaN, there will be more checkboxes than just these two