JSFiddle - React, Tailwind, and code Playground

HTML

<ol>
<li><label for="start-date">Start Date:</label>
<input name="start-date" id="start-date" class="date-pick dp-applied"></li>
<li><label for="end-date">End Date:</label><input name="end-date" id="end-date" class="date-pick"></li>
<li><label for="book_days">Days:</label><p id="book_days">5 days</p></li>
<li><label for="book_price">Total Price:</label><p id="book_price">$125</p></li>
</ol>

JavaScript

var firstDate = "19/06/2016";
var firstDateSplit = firstDate.split("/");
var first = new Date(firstDateSplit[2], firstDateSplit[1] - 1, firstDateSplit[0]);
first.setMonth( first.getMonth( ) + 1 );
var seconddate = ( first.getMonth( ) + 30 ) + '/' + first.getDate( ) + '/' + first.getFullYear( );
console.log(seconddate);