Reserved Instances vs Savings Plans: which to buy and when
7 min read · June 16, 2026 · TurboFinOps
Commitments — Reserved Instances, Savings Plans and Committed Use Discounts — are the single biggest FinOps lever: 1- or 3-year discounts of 30-70% for predictable usage. They are also the easiest to get wrong, because a commitment to spend you do not use is just a different kind of waste.
The trade-off: flexibility vs discount
Reserved Instances give the deepest discount but are the least flexible — tied to instance family, region and sometimes size. They suit stable, well-understood workloads.
Savings Plans (AWS) trade a little discount for flexibility: you commit to a dollar-per-hour of compute spend, and it applies across instance families and regions automatically. They suit changing fleets.
GCP Committed Use Discounts commit to vCPU/memory; Azure Reservations and Savings Plans mirror the AWS model.
Buy to your floor, not your peak
The cardinal rule: commit to your stable baseline — the usage you are confident persists for the term — and leave the variable top on on-demand or spot.
Layer commitments: a base of 3-year for the rock-solid floor, a 1-year layer for likely-but-less-certain usage, and on-demand for the spiky top.
Manage coverage and utilization
Two metrics matter: coverage (what share of eligible usage a commitment covers) and utilization (what share of a commitment is actually used). Low utilization means you over-bought; low coverage means money left on the table.
Track both continuously, and act on renewals before they lapse — an expiring commitment that silently rolls to on-demand is a quiet cost spike.
When in doubt, start flexible
If your fleet is changing, start with Savings Plans / shorter terms and tighten toward RIs as your baseline becomes clear. The small discount you give up is cheaper than being locked into the wrong commitment.
Frequently asked questions
- Should I buy 1-year or 3-year commitments?
- Match the term to your confidence. 3-year for the baseline you are certain persists (deepest discount), 1-year for usage that is likely but less certain. Layering both plus on-demand handles the variable top.
- What happens if I do not use a commitment I bought?
- You still pay for it — an underutilized commitment is wasted spend. That is why you commit to your stable floor, not your peak, and track utilization continuously.
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