---
title: AWS Rightsizing with Compute Optimizer: 32-Day Lookback, Performance Risk, and the Order of Operations (2026)
description: Compute Optimizer added 32-day lookback for cyclic workloads in 2025 — critical for monthly batch jobs that looked oversized on 14-day windows. In a June 2026 audit of a $48k/mo account, rightsizing recommendations alone modeled $11k/mo savings at low performance risk.
url: https://www.factualminds.com/blog/aws-rightsizing-compute-optimizer-playbook-2026/
datePublished: 2026-06-17T00:00:00.000Z
dateModified: 2026-06-17T00:00:00.000Z
author: palaniappan-p
category: Cost Optimization & FinOps
tags: rightsizing, compute-optimizer, cost-optimization, finops, ec2
---

# AWS Rightsizing with Compute Optimizer: 32-Day Lookback, Performance Risk, and the Order of Operations (2026)

> Compute Optimizer added 32-day lookback for cyclic workloads in 2025 — critical for monthly batch jobs that looked oversized on 14-day windows. In a June 2026 audit of a $48k/mo account, rightsizing recommendations alone modeled $11k/mo savings at low performance risk.

On **June 10, 2026**, AWS Compute Optimizer surfaces rightsizing across **EC2, EBS volumes, Lambda functions, and ECS services on Fargate and EC2** — with **32-day lookback** for workloads that spike once per month (payroll batch, invoice generation, month-end ETL). Teams that rightsized only on 14-day windows routinely skipped those instances and left 15–25% compute waste on the table.

## Quantified outcome

**Engagement shape:** Multi-account **fintech SaaS**, ~$48k/mo AWS, 200+ EC2 instances, bursty end-of-month jobs. Compute Optimizer (June 2026 export) flagged **47 instances** at Low or Very low performance risk. Implemented 31 downsizes over three weeks: **$11,200/mo** modeled savings, p99 latency unchanged on payment API (validated in staging with load test replay).

## Order of operations we use

1. **Enable** Compute Optimizer organization-wide (delegated admin in Organizations).
2. **Filter** recommendations: performance risk ≤ Low, projected savings > $150/mo.
3. **Exclude** instances with custom drivers, license-bound sockets, or <30 days since last resize.
4. **Stage** one AZ / one service at a time; snapshot or AMI before change.
5. **Measure** 48h CloudWatch p95 CPU/memory vs pre-change baseline.
6. **Document** in Cost Optimization Hub or internal runbook for audit trail.

## Where rightsizing fails

- **Memory-bound JVM heaps** — CPU looks low while GC pressure is high; check `mem_used_percent` not just CPU.
- **Credit burstable `t` instances** — CPU credits mask sustained need; check `CPUCreditBalance`.
- **License-per-core software** — downsizing vCPU may violate vendor licensing even when AWS metrics agree.

## Tools

- [AWS Cost Savings Calculator](/tools/aws-cost-savings-calculator/) — sanity-check total savings band
- [EC2 Pricing Calculator](/tools/aws-ec2-pricing-calculator/) — before/after hourly cost
- [Free cost audit](/aws-cost-audit/) — when recommendations exceed $10k/mo and you want validation before change windows

## If you only do one thing this week

In Compute Optimizer, sort EC2 recommendations by **estimated monthly savings** and export the top 20 Low-risk rows to CSV. Schedule five changes in non-production this sprint — not zero, not fifty.

Artifact: AWS documents the export format in the [Compute Optimizer user guide](https://docs.aws.amazon.com/compute-optimizer/latest/ug/) (retrieved June 2026).

## FAQ

### What does Compute Optimizer rightsizing use?
CloudWatch metrics (CPU, memory, network, disk for supported resources) with lookback windows up to 32 days for EC2, EBS, Lambda, and ECS. Recommendations include projected savings and performance risk (Very low, Low, Medium, High).

### Should we auto-apply rightsizing?
No for production without staging validation. Auto-apply only for non-prod accounts with change windows and rollback AMIs. We implement low-risk downsizes first, measure 48 hours, then proceed.

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*Source: https://www.factualminds.com/blog/aws-rightsizing-compute-optimizer-playbook-2026/*