The number of spent surplus credits that are not paid down by earned CPU credits, and which thus incur an additional charge.

Spent surplus credits are charged when any of the following occurs:
- The spent surplus credits exceed the maximum number of credits that the instance can earn in a 24-hour period. Spent surplus credits above the maximum are charged at the end of the hour;
- The instance is stopped or terminated;
- The instance is switched from unlimited to standard.