I purchased an Amazon EC2 Reserved Instance, but it's being utilized in a way I didn't expect. Why is my Reserved Instance applying to my usage in the way it is?

If your Reserved Instance isn't applying to any usage at all, see My EC2 Reserved Instance isn't applying to my billing—why?

The most common reason that a Reserved Instance isn't applying to the instance you expect is that the terms of the Reserved Instance do not match. The Reserved Instance that you purchase must match the platform, type, size (or size footprint), region (if applicable), and tenancy of an instance for it to apply. Check the terms of your Reserved Instance and the instance it applies to.

If the Reserved Instance terms match the instance you intended it to apply to, and it's still not applying as you expected, consider the following additional conditions:

  • In an organization's consolidated bill, the account that originally purchased the Reserved Instance receives the billing benefit first. If the purchasing account doesn't have any instances that match the terms of the Reserved Instance, it is assigned to any matching usage on another account in the organization.
  • For size-flexible Reserved Instances, the billing benefit is not necessarily applied to an instance exactly matching the terms of the Reserved Instance before it matches a complementary grouping of smaller instances. For example, if you run an m3.large instance and two m3.medium instances, and you purchase a Reserved Instance for an m3.large instance, the Reserved Instance billing benefit might apply to either of these groups of instances. To see which instances are covered by Reserved Instances on your account, use one of the bill reporting options here: How do I tell if my Reserved Instances are being used?

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Published: 2017-06-26