Dev & engineering · free calculator
EC2 instance rightsizing savings
Compute monthly + 3-year savings from rightsizing under-utilized EC2 instances vs reserved instances vs savings plans.
Annual savings
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- Current annual cost$40,320
- Annual savings (rightsizing)$20,160
- Annual savings (rightsizing + SP)$27,216
EC2 rightsizing — the easy 30-50% bill cut
Most production EC2 fleets run at 15-30% average CPU utilization. The remaining capacity is paid-for slack. Rightsizing brings utilization to 50-65% (still safe) and cuts spend 30-60% per instance.
The two-step move
- Rightsize — analyze CloudWatch metrics, downsize over-provisioned instances
- Cover with Savings Plans — Compute Savings Plans (1-yr or 3-yr commit) on the right-sized baseline
Default scenario: 12 instances × $280/mo × 12 = $40,320/yr. Rightsizing 50% × 80% of fleet = $16k savings. Layer Savings Plan on remaining = $8.5k more. Total annual savings: ~$24,500.
Where rightsizing is dangerous
- Burst workloads: instances that spike during peak need headroom. Average CPU misleads. Look at p99.
- Memory-bound apps: CPU utilization is irrelevant. Switch to memory-optimized rather than smaller.
- Network-bound apps: smaller instances = lower bandwidth caps. Verify network requirements.
- Database instances: never rightsize aggressively. Memory + connection limits scale with size.
Savings Plan vs Reserved Instance
Compute Savings Plans are strictly better than RIs for most workloads:
- Cover any instance family (vs RI which is family-locked)
- Cover Lambda + Fargate too (RIs only cover EC2)
- Match-rate flexibility (RIs require exact match)
Use RIs only for very stable, single-family workloads where the slight discount edge matters.
The 3-year math
3-year All-Upfront Savings Plan = ~50-55% off on-demand. If your usage is stable, this saves 18-22% over 1-yr No-Upfront. Cash up-front is the trade-off; capital-constrained startups stick with 1-yr.
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