Committing to AWS usage via Reserved Instances (RIs) or Savings Plans is the single highest-impact lever most AWS customers can pull to reduce costs. The potential savings are substantial — up to 72% off on-demand pricing — but the commitment comes with real financial risk if you make the wrong choices. Locked into the wrong instance type as your architecture evolves, or committed to more than you use, and discounts become expensive mistakes.
At $15,000/month in EC2 spend, a 1-year Compute Savings Plan covering $12,000/month of that spend at a 33% discount saves $47,520/year. That's real, immediate, low-risk savings — but only if you set it up correctly. This guide gives you the full picture to make confident purchasing decisions.
Understanding the Commitment Products
AWS offers several distinct commitment products. Understanding what each covers and how they differ is essential to making smart purchasing decisions.
EC2 Reserved Instances
The original AWS commitment product. You commit to a specific EC2 instance family and region (Convertible RIs) or a specific instance type, region, OS, and tenancy (Standard RIs). In exchange, AWS discounts that instance's hourly rate.
- Standard RIs: Maximum discount (up to 72%), zero flexibility. You're locked into the exact instance type, region, and OS. Cannot be modified to a different instance type.
- Convertible RIs: Slightly lower discount (up to 54%), but can be exchanged for a different instance type within the same instance family. Useful if you're migrating from m5 to m6i or m7g (Graviton).
- Scope: EC2 only. Cannot be applied to Fargate, Lambda, or any other service.
Compute Savings Plans
The most flexible commitment product. You commit to a dollar amount of compute usage per hour (e.g., $10/hr). AWS automatically applies the discount to any qualifying usage, in any region, on any instance family, for EC2, Fargate, and Lambda.
- Maximum discount: Up to 66% (3-year), up to 40% (1-year)
- Flexibility: Applies to any EC2 instance type, Fargate tasks, and Lambda functions — no lock-in to specific types
- Best for: Teams that are still optimizing their instance mix, migrating to Graviton, or using Fargate/Lambda
EC2 Instance Savings Plans
A hybrid between Standard RIs and Compute Savings Plans. You commit to a specific EC2 instance family in a specific region (e.g., m5 in us-east-1), but the commitment is flexible within that family across any size and OS.
- Maximum discount: Up to 72% — same as Standard RIs
- Flexibility: Any instance size within the family (m5.large, m5.xlarge, m5.4xlarge) and any OS. But locked to one instance family and region.
- Best for: Teams stable on a specific instance family but still resizing within it
RDS Reserved Instances
Reserved Instances for Amazon RDS. Committed to a specific DB engine (PostgreSQL, MySQL, Aurora, etc.), instance class, and region. Can save up to 69% vs on-demand RDS pricing.
ElastiCache and Other Service RIs
Reserved Instances are also available for ElastiCache, Redshift, OpenSearch, and other services. The mechanics are the same — commit for 1 or 3 years, get a discount. Each service has its own RI product with service-specific flexibility rules.
Head-to-Head Comparison
| Product | Services Covered | Max Discount (1yr) | Max Discount (3yr) | Flexibility | Best Use Case |
|---|---|---|---|---|---|
| Compute Savings Plan | EC2, Fargate, Lambda | 40% | 66% | Any instance type/family/region | General EC2 + mixed workloads |
| EC2 Instance Savings Plan | EC2 only | Up to 72% | Up to 72% | Any size within one family + region | Stable instance family, still resizing |
| Standard RI | EC2 only | 40% | 72% | None — exact type/OS/region locked | Frozen instance configurations |
| Convertible RI | EC2 only | 31% | 54% | Exchange to other types in same family | Migrating between generations (m5 → m7g) |
| RDS RI | RDS only | 40% | 69% | Engine + class locked | Stable production databases |
Real-World Savings Example: $15,000/Month EC2 Spend
Let's work through a concrete example. Your team spends $15,000/month on EC2 on-demand, distributed across m5 and c5 instances in us-east-1. You've just completed a rightsizing exercise and your fleet is now correctly sized. How should you structure your commitments?
Approach 1: 1-Year Compute Savings Plan, No Upfront
Commit to $10/hr ($7,200/month at the discounted rate, covering ~$10,500/month of on-demand spend).
Discount: 33%
Annual savings: ~$3,960/month × 12 = $47,520/year
Risk: Low. If your architecture changes, the Savings Plan covers any EC2 usage automatically.
Approach 2: 1-Year EC2 Instance Savings Plan (m5 family, us-east-1) + 1-Year Compute Savings Plan for the rest
If 70% of your spend is m5 instances: commit $8,000/month as an EC2 Instance Savings Plan at 40% discount, remainder as Compute Savings Plan at 33%.
Annual savings: ($8,000 × 0.40 × 12) + ($4,500 × 0.33 × 12) = $38,400 + $17,820 = $56,220/year
Risk: Medium. If you migrate from m5 to m7g (Graviton), your EC2 Instance Savings Plan won't cover m7g instances — the Compute Savings Plan portion would, but you'd have unused EC2 Instance Savings Plan commitment.
The commitment trap: The biggest RI/Savings Plan mistake is over-committing. If you commit to $15/hr but only use $12/hr, you're paying for $3/hr of unused commitment. Always commit to your minimum baseline usage, not your average. Cover the floor with commitments, let the ceiling run on-demand. AWS Cost Explorer's Savings Plan recommendations use 7-day or 30-day lookback precisely to identify this baseline.
Payment Options: No Upfront vs. Partial vs. All Upfront
For both RIs and Savings Plans, you choose a payment option that affects the discount rate and your cash flow:
- No Upfront: Pay monthly for the committed amount. Lowest discount rate. Best if your cash flow is constrained.
- Partial Upfront: Pay ~50% upfront, remainder monthly. Higher discount than No Upfront. Good middle ground.
- All Upfront: Pay the full committed amount upfront. Highest discount rate. Best if you have available cash and want maximum savings.
For a 1-year m5.2xlarge Standard RI in us-east-1 (Linux):
- On-Demand: $0.384/hr ($2,765/month)
- No Upfront RI: $0.233/hr ($1,678/month) — 39% savings
- Partial Upfront RI: $0.223/hr ($1,606/month) — 42% savings
- All Upfront RI: $0.214/hr ($1,541/month) — 44% savings
The incremental savings from All Upfront vs No Upfront on a single instance is ~$137/month. The ROI on the upfront payment depends on your cost of capital — for most companies, the incremental savings easily justify the upfront payment.
Managing Your RI/SP Portfolio
Purchasing commitments is the beginning, not the end. You need to actively manage your RI/SP portfolio:
- Track utilization: In Cost Explorer → Savings Plans → Utilization, monitor whether your commitments are being fully utilized. A Savings Plan at 80% utilization means 20% of your commitment is wasted. Target >90% utilization.
- Watch expiration dates: RIs and Savings Plans expire at the end of their term. Without action, you revert to on-demand pricing. Set calendar reminders 60–90 days before expiration to evaluate renewal.
- Consider the RI Marketplace: Standard RIs can be sold on the AWS RI Marketplace if your needs change. You typically recover 80–95% of the remaining value, which significantly reduces the risk of over-committing.
Get a Personalized Commitment Strategy
Hero Savings analyzes your actual AWS usage patterns and generates a precise Savings Plan and RI purchasing strategy — showing you exactly which commitments to buy, in what amounts, to maximize savings without over-committing.
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