function due_date() {    
  var d = parseInt(document.getElementById('day').value);
  var m = parseInt(document.getElementById('month').value);
  var y = parseInt(document.getElementById('year').value);
  //	var c = parseInt(document.getElementById('cycle').value);
  var c = 28;
    var starto = new Date();
  starto.setDate(d);
  starto.setMonth(m-1);
  starto.setYear(y);
  var daymsecs = 60*60*24*1000;
  starto.setTime(starto.getTime() + ((c * daymsecs) - daymsecs*14));
  var dudate = new Date();
  dudate.setTime(starto.getTime() + daymsecs*266);
  document.getElementById('due').value = formatted_date(dudate);
}

function formatted_date(date) {
  var month = new Array("January", "February", "March", "April", "May", "June", "July", "August", "September", "October",
  	"November", "December");
  var y = date.getYear()+1900;
  if ((y > 100) && (y <1900)) y+=1900;
  if (y == 3900) y = 2000;
  return("" + month[date.getMonth()] + " " + date.getDate() + ", " + y);
}