Usage billing

Except for DynamoDB reservations, which are billed based on throughput, reservations are billed for every clock-hour during the term you select, regardless of whether an instance is running or not. A clock-hour is defined as the standard 24-hour clock that runs from midnight to midnight and is divided into 24 hours (for example, 1:00:00 to 1:59:59 is one clock-hour).

A Reserved Instance billing benefit can be applied to a running instance on a per-second basis. Per-second billing is available for instances using an open-source Linux distribution, such as Amazon Linux and Ubuntu. Per-hour billing is used for commercial Linux distributions, such as Red Hat Enterprise Linux and SUSE Linux Enterprise Server.

A Reserved Instance billing benefit can apply to a maximum of 3600 seconds (one hour) of instance usage per clock-hour. You can run multiple instances concurrently, but can only receive the benefit of the Reserved Instance discount for a total of 3600 seconds per clock-hour. Instance usage that exceeds 3600 seconds in a clock-hour is billed at the On-Demand Instance rate.

For example, if you purchase one m4.xlarge Reserved Instance and run four m4.xlarge instances concurrently for one hour, one instance is charged at one hour of Reserved Instance usage and the other three instances are charged at three hours of On-Demand Instance usage.

However, if you purchase one m4.xlarge Reserved Instance and run four m4.xlarge instances for 15 minutes (900 seconds) each within the same hour, the total running time for the instances is one hour, which results in one hour of Reserved Instance usage and 0 hours of On-Demand Instance usage.

Figure 3 – Running four instances for 15 minutes each in the same hour

If multiple eligible instances are running concurrently, the Reserved Instance billing benefit is applied to all the instances at the same time up to a maximum of 3600 seconds in a clock-hour. Thereafter, the On-Demand Instance rates apply.

Figure 4 – Running four instances concurrently over the hour

You can find out about the charges and fees to your account by viewing the AWS Billing and Cost Management console. You can also examine your utilization and coverage, and receive reservation purchase recommendations, via AWS Cost Explorer. You can dive deeper into your reservations and Reserved Instance discount allocation via the AWS Cost and Usage Report.

For more information on Reserved Instance usage billing, see Usage Billing.