AWS bill line item
UnusedBox:m5.large
The instance-hours of an On-Demand Capacity Reservation that were held open but never had an instance launched into them. These bill at the full On-Demand rate for empty, reserved slots.
Unused Capacity Reservation
Verified against official AWS documentation last checked
Why it shows up
Appears whenever a Capacity Reservation is sized larger than the instances running against it. For example, ten slots reserved in an AZ for a launch event, but only two in use: the other eight bill as unused capacity every idle hour.
Easy to miss because it's a distinct usage type from the reservation itself and from any Reserved Instance discount. Capacity Reservations guarantee capacity but carry no billing discount of their own, so idle slots cost full price.
How to cut it
- Size Capacity Reservations to actual peak concurrent instance count, not a padded estimate.
- Scope reservations to the exact window capacity is needed (a launch event, a DR test) and delete them afterward.
- Monitor reservation utilization to alert on reservations sitting persistently under-used.
How to read this code
:instanceType suffixThe specific instance type or size a charge applies to, e.g. BoxUsage:m5.large. One line per distinct type in use.
Source
Source: AWS docs →Found UnusedBox:m5.large on your own bill?
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