You pay for two things: the hourly compute costs for the virtual network gateway, and the egress data transfer from the virtual network gateway. Pricing information can be found on the Pricing page.
Virtual network gateway compute costs
Each virtual network gateway has an hourly compute cost. The price is based on the gateway SKU that you specify when you create a virtual network gateway. The cost is for the gateway itself and is in addition to the data transfer that flows through the gateway.
Data transfer costs
Data transfer costs are calculated based on egress traffic from the source virtual network gateway.
- If you are sending traffic to your on-premises VPN device, it will be charged with the Internet egress data transfer rate.
- If you are sending traffic between virtual networks in different regions, the pricing is based the region.
- If you are sending traffic only between virtual networks that are in the same region, there are no data costs. Traffic between VNets in the same region is free.