When you prepay for compute needs with Amazon Elastic Compute Cloud (Amazon EC2) Reserved Instances, Amazon Relational Database Service (Amazon RDS) Reserved Instances, Amazon Redshift Reserved Instances, or Amazon ElastiCache Reserved Cache Nodes and are enrolled in a paid AWS Support plan, the one-time (upfront) charges for the prepaid resources are included in the calculation of your AWS Support charges in the month you purchase the resources. In addition, any hourly usage charges for reserved resources are included in the calculation of your AWS Support charges each month.
If you have existing reserved resources when you sign up for a Support plan, the one-time (upfront) charges for the reserved resources, prorated over the term of the reservation, are included in the price calculation for the first month of AWS Support. For example, if you purchase a three-year reserved instance on January 1 and sign up for the Business support plan on October 1 of the same year, 75% of the upfront fee you paid in January is included in the calculation of Support costs for October.