jQuery DatePicker and you have one calendar and you want to set the date on the next calendar:

<!-- datepicker load second date-->
<script type="text/javascript">

$().ready(function () {
    $('.calendar').datepicker({
        numberOfMonths: 2,
        showButtonPanel: true,
        showOn: 'both'
      });
   
    //get date1 and set date2. date2 is 1d after date1 
    $('#date1').change(function () {
        var nextDayDate = $('#date1').datepicker('getDate', '+1d');
        nextDayDate.setDate(nextDayDate.getDate() + 1);
        $('#date2').datepicker('setDate', nextDayDate);
    });
});