The S3 Cost Optimization Playbook

Most S3 bills are wrong, and the fix takes an afternoon. The data sits in the most expensive class AWS offers (S3 Standard, $0.023/GB-month), nobody set a lifecycle policy, incomplete multipart uploads are silently billing for storage you can't even see in the console, and every byte your EC2 fleet pulls from S3 is routed out through a NAT Gateway when a free VPC Gateway Endpoint would do the same job for $0. None of this needs an architecture rewrite. It needs a checklist run in the right order. Here is the order. The savings depend entirely on your access pattern — I will not promise you a number I can't see — but the mistakes below are so common that the question is usually how much , not whether . One number is just arithmetic: cold data that moves from S3 Standard ($0.023/GB-month) to Glacier Deep Archive ($0.00099/GB-month) drops about 96% on the storage line for those bytes, and on an observability platform I ran — logs aged past 90 days into Deep Archive — that is exactly the lever that did the work. S3 cost optimization is the same boring discipline as the rest of the bill: see it, then decide what each byte should actually cost. First, see the bill before you touch it You cannot optimize what you cannot measure, and S3's default billing view tells you nearly nothing useful. Turn on S3 Storage Lens before anything else. The free tier gives you 62 metrics at the bucket level with 14 days of history, and crucially it includes cost-optimization metrics out of the box — including "Incomplete multipart upload bytes greater than 7 days old," which is the single most common source of money disappearing into storage nobody knows exists ( AWS S3 Storage Lens docs , accessed 2026-06-18). Storage Lens free metrics answer the three questions that decide everything that follows: Which buckets hold the most bytes? What storage class is that data sitting in right now? Where are the incomplete multipart uploads? For deeper per-prefix analysis or a longer history, Advanced