NAT Gateway charges a per-gigabyte data processing fee on all traffic that passes through it — in either direction — regardless of whether the destination is the public internet or another AWS service in the same region. This per-GB charge is separate from and additive to the hourly provisioning cost, and for workloads with meaningful throughput, it quickly becomes the dominant cost component. In many US regions, the data processing charge matches the hourly rate (e.g., $0.045/GB in US East Ohio), meaning that once monthly traffic exceeds roughly 720 GB, data processing costs surpass the baseline hourly charges entirely. For internet-bound traffic, a compounding effect occurs: hourly provisioning, per-GB data processing, and standard data transfer out charges all apply simultaneously — creating a combined variable cost that can reach $0.135 per GB or more.

This cost structure is frequently underestimated during architecture planning. Teams designing VPC layouts often account for the hourly cost of NAT Gateways but overlook how significantly the per-GB processing fee scales with traffic volume. The result is that workloads routing high-throughput traffic to AWS services like S3, DynamoDB, container registries, or logging endpoints through NAT Gateway incur substantial and avoidable data processing charges. Gateway VPC endpoints for S3 and DynamoDB carry no hourly or data processing charges at all, and interface VPC endpoints for other AWS services process data at a fraction of the NAT Gateway rate. Without deliberate traffic routing decisions, NAT Gateway data processing can quietly become one of the largest line items on an AWS bill.