JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.14/themes/smoothness/jquery-ui.css">
<input type="text" class="firstcal">
<input type="text" class="secondcal">

CSS

body
{
    font-size: 10px;
}

JavaScript

$(function() {
    $(".firstcal").datepicker({
        dateFormat: "dd/mm/yy",
        onSelect: function(dateText, instance) {
            date = $.datepicker.parseDate(instance.settings.dateFormat, dateText, instance.settings);
            date.setMonth(date.getMonth() + 48);
            $(".secondcal").datepicker("setDate", date);
        }
    });
    $(".secondcal").datepicker({
        dateFormat: "dd/mm/yy"
    });
});