If you're on a month-to-month plan: On the 16th of each month, you'll get billed for the following month's box.
If you're on a longer prepaid plan: You'll be billed on the 16th of the month every 3, 6, or 12 months, according to the prepaid subscription term you’ve chosen. If you skip any boxes on a prepaid plan, your remaining boxes will simply move to the following month. Your purchased boxes will never expire, and your renewal will not go through until you have received all of your prepaid boxes.
Please note that each month's renewal pays for the following month's box (e.g., the January 16th renewal covers the box shipped in early February, the February 16th renewal covers the box shipped in early March, and so on), so if the final box on your 6-month prepaid plan is shipping in early May, for instance, your renewal will go through on May 16th for June's–November's boxes.
Regular subscriptions renew automatically but can be canceled whenever you'd like (without forfeiting any boxes you’ve already paid for), and you can skip any boxes you'd rather not receive through your account. Gifts do not auto-renew.