$(document).ready(function(){
      var dp = $("#period_date").datepicker({
        buttonImage: '/wp/wp-content/static/img/calendar.png',
        buttonImageOnly: true,
        showOn: 'both',
        dateFormat: 'mm/dd/yy',
      });
      dp.datepicker('setDate', new Date);

      var pl = $('#period_length');
      for(var i = 22; i<46; i++) {
        pl.append('<option value="' + i +'">' + i + '</option>');
      }
      pl.val(28);

      $("#calculate").click(function() {

        var menstrual = new Date($("#period_date").val());
        var ovulation = new Date();
        var due       = new Date();
        var today     = new Date();

        var luteal = 14;
        
        ovulation.setTime(menstrual.getTime() + $("#period_length").val()*86400000 - luteal*86400000);
        due.setTime(ovulation.getTime() + 266*86400000);

        var age = 14 + 266 - (due - today)/86400000;
        var weeks = parseInt(age/7);
        var days = Math.floor(age % 7);

//  alert("due: " + due + ", weeks: " + weeks + ", days: " + days);
      });
    });