Unconverted Convertible EC2 Reserved Instances

Jason DiDomenico

Service Category

Compute

Cloud Provider

AWS

Service Name

AWS EC2

Inefficiency Type

Misconfigured Reservation

Explanation

Convertible Reserved Instances provide valuable pricing flexibility — but that flexibility is often underused. When EC2 workloads shift across instance families or OS types, the original RI may no longer apply to active usage. If the RI is not converted, the customer continues paying for unused commitment despite having the ability to adapt it.

Because conversion is a manual process and requires matching or exceeding the original RI’s value, many organizations fail to optimize their coverage. Over time, this leads to growing pools of ineffective RIs that could have been aligned to real workloads.

Relevant Billing Model

Convertible RIs are billed hourly based on the original reservation terms
Charges continue regardless of actual instance usage
RIs must be **actively converted** to align with changing usage — past underutilization is not refunded

Detection

Identify Convertible RIs with low utilization over a trailing period
Compare current EC2 usage to the instance types, families, and configurations reserved under each RI
Highlight RIs that are eligible for conversion but remain mismatched to actual compute patterns
Evaluate how much unused commitment could be recovered through a conversion

Remediation

Use the AWS Management Console or CLI to convert unused Convertible RIs to match current EC2 instance usage
Ensure the new reservation configuration has equal or greater value, as required by AWS
Monitor usage regularly to identify when new conversions may be needed
Build RI optimization reviews into quarterly infrastructure hygiene practices to prevent recurring waste

Relevant Documentation