Quick Answer — How Much Data Does a VPN Use?
A VPN does not change how much content you request; it changes how much wrapping each packet carries. The extra is a fixed proportion of whatever goes through the tunnel: Total = Baseline + (Baseline × VPN share × overhead).
Measured overheads differ by protocol far more than most people expect. On 60 GB of baseline monthly usage with everything routed through the tunnel:
- WireGuard, 4.53% — adds 2.72 GB, total 62.72 GB
- IKEv2, 7.5% — adds 4.50 GB, total 64.50 GB
- OpenVPN UDP, 17.23% — adds 10.34 GB, total 70.34 GB
- OpenVPN TCP, 19.96% — adds 11.98 GB, total 71.98 GB
The spread is the story: OpenVPN over TCP costs 4.4 times what WireGuard does on identical traffic, and the gap is a setting in your VPN app rather than anything about how you use the internet. OpenVPN over TCP is worst because it stacks its own reliability and retransmission layer on top of a transport that already provides one.
Two caveats before you use these numbers. Overhead applies only to tunnelled traffic, so split tunnelling scales it down proportionally — and none of this affects the *content* you download, only the packaging around it.