I was able to resolve the issue by doing this and incrementing the getMonth() call and setting it to the variable before displaying the date in a formatted way.
var nDate = new Date(inputBox.value);
nDate.setMonth( nDate.getMonth( ) + 1 );
inputBox1.value = (nDate.getMonth() + 1) + "/" + (nDate.getDate()) + "/" + (nDate.getFullYear());