Transit Gateway Cost

Per-attachment + per-GB.

Overview

AWS Transit Gateway charges per attachment per hour plus per GB processed through the gateway. At small scale the bill is invisible; at multi-VPC scale with cross-region peering it becomes a structural line item. The discipline is matching architecture to actual connectivity need: TGW for hub-and-spoke, VPC peering for point-to-point, and VPC endpoints for AWS-service traffic that should never touch TGW.

• Per-attachment plus per-GB pricing. Hourly cost per attachment compounds across VPCs, VPNs, and Direct Connect; per-GB processing fee on top.
• Attachment count grows fast. Hub-and-spoke architectures multiply attachments. Each VPC, each VPN, each DX connection.
• Data processing fee. Per-GB through TGW. Stacks on top of the inter-AZ and inter-region transfer fees.
• Cross-region peering plus VPC endpoints alternative. Inter-region peering carries premium pricing; VPC endpoints bypass TGW entirely for S3 and DynamoDB.

The approach

Three habits keep Transit Gateway cost matched to actual connectivity need: pick the right primitive (TGW, VPC peering, or endpoints) per traffic pattern, monitor traffic per attachment, and review the architecture quarterly to catch unused or chatty attachments.

• Right architecture per pattern. TGW for hub-and-spoke; VPC peering for two-VPC connections; VPC endpoints for AWS-service traffic.
• Traffic awareness per attachment. Per-VPC the data volume. The chatty attachments surface as cost lines.
• VPC endpoints for S3 and DynamoDB. Bypass TGW entirely. Direct savings on every byte of S3 and DynamoDB traffic.
• Quarterly review plus documented rationale. Standing review catches drift; per-attachment the why-this-architecture documented.

Why this compounds

Each correctly-shaped TGW architecture cuts the bill every month for the lifetime of the workload. The team’s networking economics fluency deepens; new VPCs ship with the right connectivity primitive on day one.

• Cost efficiency. Right architecture cuts the per-GB and per-attachment fees that compound silently.
• Connectivity quality. Right primitive for the pattern. Hub-and-spoke fits TGW; point-to-point fits VPC peering; AWS services fit endpoints.
• Operational hygiene. Quarterly review catches stale attachments before they become structural cost.
• Year-one investment, year-two habit. First architecture review is heavy lift. By year two, networking-economics thinking is part of design review.