Data Rollover

I have an AT&T Z432 Go Phone.  If I have an AUTO RENEW on my data package, and if I have plenty of cash in the phone account, does the remaining data for one month period (e.g., my Go Phone has a $5/5MB data plan) ROLLOVER into the next month, or do I lose the remaining data?   (I know I lose the remaining data if I do not auto renew or manual renew the data package before the month runs out.)

Thanks.

Mike Bailey