"Idle" sounds free. It is not. Some of the most reliable waste in an AWS account comes from resources that are running, doing almost nothing, and billing you the full rate anyway. The frustrating part is that none of them is expensive enough on its own to trigger a second look, so they survive for months. Put a real monthly number on each and they stop looking harmless.
Here are the three most common idle-but-billing resources, roughly what each costs, and how to find yours.
Idle NAT gateway: roughly $32+ per month, before traffic
A NAT gateway bills two ways: an hourly charge just for existing, plus a per-GB data processing charge for traffic through it. The hourly charge alone is about $0.045 per hour in most regions, which is roughly $32 a month per gateway whether or not a single byte flows through it.
The waste pattern: a NAT gateway left behind in a region or VPC you migrated out of, or one provisioned per-AZ "for high availability" in an environment that no longer needs all of them. Each idle one is $32+ a month for nothing, and teams often have several.
