Need days since record added calculation- help

Need days since record added calculation- help

In my app, I need to change the status of a record from Available to Unavailable after 30 days pass from the date when the record was created.  How do I do this?  I was trying to use this formula, but I cant seem to figure out how to get the date added from the system:

((zoho.currentdate - DATE ADDED FROM SYSTEM)  /  (1000  *  60  *  60  *  24))

Help?