What's the correct php path to externally link from a subfolder into functions file

To keep my functions clean, I reference some php code externally into a subfolder I created called "includes". The link below works on my local wamp server with multisite installed:

include ('includes/referencefile.php');

But when I try to upload it to my hostgator hosting, it doesn't seem to find the path. Could you provide me with the correct or ideal path?