> Promotional Credit

> 5.8 As of March 6, 2015, redemption of promotional credit is limited to 12 months from the date of issue (unless otherwise stated), at which time the credit will expire. Upon redemption, promotional credit expires after 12 months unless otherwise defined in the terms of the promotion. For instances where promotional credit was issued or redeemed prior to March 6, 2015, that credit will expire on March 6, 2016.

> 5.9 Only one promotional code is permitted per customer, and may be redeemed only by “new users,” defined as users who are within 30 days of launching their first Droplet.

Tl;dr: Grandfathered accounts with existing credit from promotions will have their credit expire in 12 months.