How are Amazon EC2 Reserved Instances that are size flexible calculated?

Last updated: 2019-04-24

I want to know how my Amazon Elastic Compute Cloud (Amazon EC2) Reserved Instances apply to my bill if the Reserved Instances are size flexible.


To find out if your Reserved Instance is size flexible, see How do Amazon EC2 Reserved Instances that are regional or size flexible work?

Size flexible Reserved Instances apply to all usage in a particular instance family. Here are a few examples of how that can work in practice:

  • Your Reserved Instance will apply to usage for any instance in its family of its same size or smaller. For example, if you purchase a Reserved Instance for an m3.large instance, the Reserved Instance also applies to m3.medium instances.
  • Multiple smaller Reserved Instances also combine to apply to larger instances. For example, if you purchase a Reserved Instance for two m3.large instances, the Reserved Instances are combined to cover an m3.xlarge instance, provided that neither of the Reserved Instances already applies to an m3.large instance.

Reserved Instances apply automatically to your billing. You can't designate which specific instances receive the benefit Reserved Instances.

If you're in an organization with multiple accounts under a consolidated bill, additional considerations can apply. For more information, see How is the pricing benefit of a Reserved Instance applied across an organization's consolidated bill?

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