Why does my AWS bill show Amazon EC2 Reserved Instance costs that I didn't expect?

Resolution

If your RI discount isn't applied to the instance in a way that you expect, then review the terms of your RI. For more information, see Why isn't my Reserved Instance applying to my AWS billing?

If your RI is active and matches the specification of a running On-Demand Instance, then use Cost Explorer to analyze your cost and usage.

If your Cost and Usage Reports still show unexpected results, then see the following common RI bill scenarios.

RI discount is applied inconsistently in a consolidated bill

RI discounts are applied differently in an organization's consolidated bill, depending on whether RI sharing is turned on or off. For more information, see How is the pricing benefit of a Reserved Instance applied across an organization's consolidated bill?

RI benefit isn't applied to the matching instance

For size-flexible RIs, the billing benefit may be applied to a complementary grouping of smaller instances instead of the instance set by the RI term. For example, if you run an m3.large instance and two m3.medium instances, then the billing benefit might apply to either of these groups of instances. To verify which instances are covered by RIs, see How do I find out if my Amazon EC2 Reserved Instances are being fully used?