JSFiddle - React, Tailwind, and code Playground
by baacke
HTML
<label>To:</label><input id="to" value="04/21/2014">
<br>
<label>From:</label><input id="from" value="">
CSS
label {display: inline-block;
width: 45px}
JavaScript
$('#from').val( subtractDays($('#to').val(), 48) );
function subtractDays(startDate, daysToSubtract){
startDate = startDate.split("/");
var newDate = new Date(startDate[2], startDate[0], startDate[1])
return newDate - daysToSubtract;
}