<script>
function getClientTimezone(){  
  var oDate = new Date();  
  var nTimezone = -oDate.getTimezoneOffset() / 60;  
  return nTimezone.toFixed(2);  
}  
alert(getClientTimezone());
</script>

<script type="text/javascript">
    var d = new Date();
    document.write(-d.getTimezoneOffset()/60);
</script>