Meaning of "reservation_NetUnusedRecurringFee" line item in an AWS bill or Cost and Usage Report

Products

• CloudHealth

Issue/Introduction

This is regarding RI costs that are not being utilized.  Reserved Instances are a commitment and are paid for regardless of they are utilized. 

Resolution

This means that if you're not fully utilizing an RI, you're still paying for it, which is what the Reservation_NetUnusedRecurringFee reflects.
 
The most effective way to reduce your Reservation_NetUnusedRecurringFee is to ensure that you're fully utilizing your RIs.