AWS · Free tool
AWS Transit Gateway cost calculator
The hub-and-spoke tax on multi-VPC AWS. Plug in attachments and monthly data processed, and see the real bill plus the cross-AZ surprise that shows up under EC2 data transfer rather than the TGW line.
Estimated monthly TGW bill
$0
$0 per year
Attachment cost
$0
15 attachments × 730 hours × $0.05/hr
Data-processing cost
$0
20,000 GB × $0.02/GB
Cross-AZ surcharge
$0
40% of 20,000 GB × $0.01/GB
If your monthly TGW bill looks high, check these first
- Unused VPC attachments still billing at $36 per month each, common after VPC decommissions.
- S3 and DynamoDB traffic crossing the TGW instead of using a Gateway VPC Endpoint.
- Two chatty VPCs (app and database) routed through TGW that should be peered directly.
- Inspection VPC pattern doubling the data-processing charge: traffic crosses the TGW twice.
- Cross-region TGW peering shipping bulk data that should run over S3 cross-region replication instead.
Why TGW shows up bigger than expected
Transit Gateway looks cheap on paper. $0.05 per attachment per hour, $0.02 per GB processed. The trap is that "data processed" counts every byte both ways, and the cross-AZ tax sits on a completely separate line under EC2 data transfer where nobody on the network team is looking.
A 12-VPC hub-and-spoke with 20 TB of monthly traffic and 40% cross-AZ runs about $1,300 per month, of which $80 is the attachment cost and the rest is data and cross-AZ. The fix is rarely throwing the TGW out, it is auditing what crosses it and peering the loud workloads.
We wrote up the most common patterns in Transit Gateway, the tax on multi-VPC.
Run this on your real account
Free 14-day audit, read-only IAM role, one-page CFO summary.
We pull your actual TGW spend, identify which VPCs are noisy, which attachments are dead weight, and which routes should be peered. The audit is free, the report is yours, and we do not chase you for an upsell call.
Frequently asked
Why is Transit Gateway often more expensive than teams expect?
Three reasons. First, every attachment is billed per hour whether or not traffic flows. Second, the per-GB processing charge applies to every byte that crosses the TGW, including same-region traffic that used to be free over peering. Third, a TGW reachable from multiple AZs incurs cross-AZ charges that are not visible in the TGW line at all, they show up under EC2 data transfer.
What is the typical regional rate?
In US regions the TGW attachment rate is around $0.05 per attachment per hour and the data-processing rate is $0.02 per GB. EU regions sit at the same rates. Asia-Pacific is slightly higher. Override the defaults if you have a Private Pricing Agreement with different rates.
Should I use Transit Gateway or VPC peering?
VPC peering is free for the connection and free for same-AZ traffic, but it does not scale, every pair of VPCs needs its own peering and route table edit. Transit Gateway scales linearly with attachments and gives you a central place to inspect or filter traffic. The break-even is usually around 6 to 8 VPCs, below that peering is cheaper, above that the operational cost of peering meshes outweighs the per-GB charge of TGW.
How do I reduce Transit Gateway cost?
Four high-leverage moves. One, route hub-and-spoke chatty traffic that should be peered directly. Two, audit cross-AZ traffic and consolidate workloads where it makes sense. Three, use VPC endpoints for AWS-native traffic so S3 and DynamoDB do not cross the TGW. Four, audit the attachment list for unused VPC attachments still billing $36 per month each. Cloud Horizon catches all four during the 14-day audit.
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