Reserved Instances vs Savings Plans: A 2026 Comparison
Three commitment instruments; very different tradeoffs. Most teams end up with the wrong mix because they pick on price alone.
The three instruments
Reserved Instances (RIs) commit to specific instance type/region/term for a discount. Savings Plans commit to dollar-spend on compute and discount whatever you run. EC2 Savings Plans are between the two.
Discount depth: RIs > EC2 SPs > Compute SPs. Flexibility: Compute SPs > EC2 SPs > RIs.
Where each wins
- RIs win for stable, identical-shape workloads. Database servers; long-lived jobs.
- EC2 SPs win when instance family changes are rare.
- Compute SPs win when you might also use Lambda or Fargate; flexibility is worth the smaller discount.
The flexibility tax
Flexibility costs. The price of saying ‘I might switch from EC2 to Fargate’ is roughly 5-8 percentage points of discount.
For most modern teams in active migration, the flexibility is worth the cost. RIs lock you into yesterday’s architecture.
Building the right portfolio
Cover 60-70% of baseline with commitments; leave 30-40% on-demand for headroom and risk. Of the commitment portion, weight toward Compute SPs unless your fleet is truly stable.
Re-evaluate quarterly. Workloads change; the optimal mix changes with them.
Antipatterns
- 100% on-demand at scale. Leaving 30%+ savings on the table.
- 100% RIs at scale. Locked into yesterday’s architecture.
- One commitment for everything. Different workloads, different right answers.
What to do this week
Three moves. (1) Pick the most exposed instance of the pattern in your environment. (2) Apply the lightest fix and measure for one week. (3) Schedule a quarterly review so the discipline does not rot.