AWS Savings Plans vs Reserved Instances: Which Discount Model Is Right for You

AWS introduced Savings Plans in 2019 as a more flexible alternative to Reserved Instances. Since then, both models have coexisted, and the decision of which to use — or what mix to use — is one of the most common questions in AWS cost optimization. The short answer: Savings Plans for flexible compute commitments, Reserved Instances for specific services and configurations where Savings Plans don't apply or provide lower discounts.

How Savings Plans Work

Savings Plans are a commitment to a specific dollar amount of AWS compute spend per hour, in exchange for a discount applied to that spend. Rather than committing to specific instance types (as RIs do), you commit to a spending rate — say $2.00/hour — and AWS applies Savings Plan discounts automatically to eligible usage up to that amount.

There are three Savings Plans types:

Compute Savings Plans apply to any EC2 instance usage, Lambda invocations, and Fargate usage, regardless of instance family, size, region, OS, or tenancy. Compute SPs provide the most flexibility with a discount of approximately 66% compared to On-Demand for 3-year, 17% for 1-year. The flexibility premium — compared to more specific commitments — is about 5 percentage points lower savings than the most specific options.

EC2 Instance Savings Plans apply to EC2 usage within a specific instance family in a specific region (e.g., M-family in us-east-1). This is less flexible than Compute SPs but provides approximately 72% savings for 3-year commitments — similar to Standard RIs with instance size flexibility. Good choice when you're confident about instance family but not specific sizes.

SageMaker Savings Plans apply specifically to SageMaker ML instance usage. Follow the same logic as other SPs but for ML workloads.

Key Differences Between Savings Plans and Reserved Instances

The fundamental difference is what you're committing to. Savings Plans are a spending commitment; Reserved Instances are a capacity commitment for specific configurations.

Flexibility: Compute Savings Plans apply automatically to any eligible usage. You don't need to predict specific instance types or regions in advance. RIs require choosing a specific instance family, size, region, OS, and tenancy at purchase time — except for instance size flexibility within some families.

Coverage scope: Savings Plans cover EC2, Lambda, and Fargate in a single commitment. RIs are service-specific — EC2 RIs don't apply to RDS; RDS RIs are a separate purchase. For mixed workloads spanning multiple compute services, Savings Plans provide simpler coverage.

Discount magnitude: For specific, committed configurations, Standard RIs typically provide slightly higher discounts than equivalent Savings Plans. The difference is approximately 2-5 percentage points. If you're very confident about your instance type and region usage pattern, RIs optimize savings slightly better than Savings Plans.

Portability and transferability: Standard RIs can be sold on the Reserved Instance Marketplace if unused. Savings Plans cannot be transferred or sold — you pay the commitment regardless of whether you use it. This makes Savings Plans less recoverable from a poor purchase decision.

Which Model for Which Situation

Use Compute Savings Plans when:

• You want to commit to a spending level but are unsure about future instance mix
• Your workload spans multiple instance families that change over time
• You have Lambda or Fargate usage that benefits from the same commitment
• You're starting with commitment discounts and want maximum flexibility to adjust

Use EC2 Instance Savings Plans or Standard RIs when:

• You're confident about your instance family usage over the commitment term
• You want to maximize discount percentage on a known stable workload
• You specifically need RDS discounts (RIs only — Savings Plans don't cover RDS)
• You might need to sell unused commitments (only possible with Standard RIs)

In practice, a mixed strategy works well for most organizations: Compute Savings Plans for general flexibility, Standard RIs for stable database workloads (RDS) and any compute workloads where you're confident about the configuration.

Monitoring Savings Plan Utilization

AWS Cost Explorer shows Savings Plan utilization — the percentage of your committed spend that was covered by actual usage. Low utilization means you're paying for commitment you're not using. High utilization (close to 100%) suggests your commitment might be too small to capture all discounts available.

Target 80-90% utilization, leaving some headroom for usage variability. A utilization rate consistently below 70% means you've over-committed. Review the coverage report to identify which usage hours weren't covered by the Savings Plan and adjust the commitment at renewal if the pattern is consistent.

Related Reading

• Reserved Instances guide — detailed RI mechanics and purchase strategy
• AWS cost optimization guide — commitment discounts in the broader cost management context
• Spot Instances guide — completing the discount model picture with spot capacity
• Billing anomaly detection — ensuring commitment investments perform as expected

FAQ

Can I have both Savings Plans and Reserved Instances active simultaneously?

Yes. Savings Plans and RIs can coexist, and AWS applies them in a specific order. RI discounts are applied first to matching usage. Savings Plan discounts are then applied to remaining usage. If you have both, make sure they're not overlapping in a way that leaves one commitment chronically underutilized.

What happens to Savings Plans if I significantly reduce my AWS usage?

You continue paying the committed hourly rate regardless of actual usage. If your usage drops below the commitment, the unused commitment is wasted. There's no refund or adjustment mechanism. This is the primary risk of over-committing — unlike RIs, you can't sell unused Savings Plans. Size your commitment to your confident baseline, not your projected peak.

Do Savings Plans apply across accounts in an AWS Organization?

Yes. Savings Plans purchased in the management account (or a delegated billing account) apply across the entire organization's compute usage. AWS applies the Savings Plan discounts to the most beneficial usage across accounts automatically. This cross-account coverage is one of the advantages of using consolidated billing through AWS Organizations.