Every RDS instance running on-demand is paying the highest rate AWS offers. RDS reserved instance pricing cuts that rate by 29% on the lowest 1-year commitment to 69% on a 3-year All Upfront term, depending on engine and instance type. For a db.r8g.xlarge PostgreSQL Multi-AZ, the difference between on-demand and 3-year reserved is roughly $4,800/year on a single instance. Across a fleet of 20, that's $96,000/year in avoidable spend.
The mechanics are more nuanced than EC2. The engine matters as much as the instance type. Size flexibility rules differ by engine. Oracle and SQL Server license model variants produce dramatically different reservation economics. Extended Support charges a significant cost item since March 2026 are specifically excluded from RI discounts, creating a trap for teams that reserve first and then discover their engine version is past end-of-standard-support.
What Are RDS Reserved Instances?
RDS reserved instances are a billing commitment: discounted hourly rate in exchange for a 1-year or 3-year term. You specify the engine, instance class, region, deployment type (Multi-AZ or Single-AZ), and payment option. AWS automatically applies the discount to matching running instances.
