Understand Amazon EC2 instance-hours billing

For more information on instance pricing based on purchase options, see Amazon EC2 pricing. If you purchase an Amazon EC2 Reserved Instance, the terms of your Reserved Instance contract can modify the way you’re billed. For more information, see What is an Amazon EC2 Reserved Instance? If you have signed up for Savings Plans, see Savings Plans FAQ.

https://aws.amazon.com/premiumsupport/knowledge-center/ec2-instance-hour-billing/