$('#datepicker').datepicker("setDate", "+3");

<script type="text/javascript">
        $(function() {
         $("#datepicker").datepicker();
         $('#datepicker').datepicker({ dateFormat: 'dd.mm.yy' });
         $('#datepicker').datepicker("setDate", "+3");
        });
        
        /* German initialisation for the jQuery UI date picker plugin. */
       jQuery(function($){
        $.datepicker.regional['de'] = {
         closeText: 'schließen',
         prevText: '&#x3c;zurück',
         nextText: 'Vor&#x3e;',
         currentText: 'heute',
         monthNames: ['Januar','Februar','März','April','Mai','Juni',
         'Juli','August','September','Oktober','November','Dezember'],
         monthNamesShort: ['Jan','Feb','Mär','Apr','Mai','Jun',
         'Jul','Aug','Sep','Okt','Nov','Dez'],
         dayNames: ['Sonntag','Montag','Dienstag','Mittwoch','Donnerstag','Freitag','Samstag'],
         dayNamesShort: ['So','Mo','Di','Mi','Do','Fr','Sa'],
         dayNamesMin: ['So','Mo','Di','Mi','Do','Fr','Sa'],
         weekHeader: 'Wo',
         dateFormat: 'dd.mm.yy',
         firstDay: 1,
         isRTL: false,
         showMonthAfterYear: false,
         yearSuffix: ''};
        $.datepicker.setDefaults($.datepicker.regional['de']);
       });
</script>