JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="//maxcdn.bootstrapcdn.com/twitter-bootstrap/2.3.2/css/bootstrap-combined.min.css">
<script src="//maxcdn.bootstrapcdn.com/twitter-bootstrap/2.3.2/js/bootstrap.min.js"></script>
<div class="progress progress-info">
    <div class="bar"></div>
</div>

JavaScript

var start = new Date(2015, 0, 1), // Jan 1, 2015
        end = new Date(2015, 7, 24), // June 24, 2015
        today = new Date(), // April 23, 2015
        p = Math.round(((today - start) / (end - start)) * 100) + '%';
    // Update the progress bar
    $('.bar').css("width", p).after().append(p);