AWS Billing and Cost Management
User Guide (Version 2.0)

Region Reserved Instances

Amazon EC2 Reserved Instances (RIs) that apply to a region provide Availability Zone flexibility and instance size flexibility. RIs that provide Availability Zone flexibility provide a discount on usage in any Availability Zone in the region. RIs that provide instance size flexibility provide a discount on usage, regardless of instance size within that family. To understand how instance size flexibility provided by your RI is applied to your usage, refer to the lineItem/NormalizationFactor and lineItem/NormalizedUsageAmount columns.


Instance size flexibility is supported only by Linux/Unix Reserved Instances with default tenancy that are assigned to a region.

For example, let’s say that you purchase one m4.xlarge RI in a given region. This m4.xlarge RI can be applied automatically to all m4 instance usage in the same region. In the following image, AWS applied the m4.xlarge to two separate m4.large instances.

The two m4.large usage line items have different ResourceIDs, and both received a discount benefit from the single m4.xlarge RI. This is shown by matching the reservationARN value across the usage and recurring monthly charge line items.

The following screenshot shows an account that has subscriptions for two m4.large RIs, with one RI in each subscription. In this example, the account uses a single instance of m4.xlarge for an hour and receives a separate discount benefit from each of the two m4.large RIs.

The single hour of m4.xlarge usage is split into two lines of 0.5 hours (both usage lines still retain the same ResourceID) because different RI subscriptions were applied to each portion of that single hour. The reservationARN for each 0.5 hour matches the corresponding RI subscription.

For more information about RI purchase options, see Billing Benefits and Payment Options in the Amazon EC2 User Guide for Linux Instances.