VPN Bandwidth Calculator
The Speed You Pay For Isn't the Speed You Get Through a VPN
Routing traffic through a VPN adds encryption headers, encapsulation, and handshake overhead to every packet, which eats into the raw bandwidth of the underlying connection. That overhead percentage varies by protocol — WireGuard is leaner than older IPsec or OpenVPN implementations — but the relationship between raw bandwidth, overhead, and effective throughput is always the same simple proportion.
The Formula
VPN encryption/protocol overhead is typically around 5–15%, but varies by protocol (OpenVPN, WireGuard, IPsec, etc.) — this calculator uses whatever overhead estimate you provide rather than assuming a fixed value.
Where This Matters
- Remote work planning — estimating real throughput for employees connecting over a corporate VPN before video calls or large file transfers.
- ISP plan sizing — deciding whether a given internet plan's raw speed leaves enough effective bandwidth after VPN overhead for the intended use.
- Protocol comparison — comparing expected effective throughput between VPN protocols with different overhead percentages.
Effective Bandwidth at Common Overhead Levels
| VPN overhead | Effective bandwidth (from 100 Mbps raw) |
|---|---|
| 5% | 95.00 Mbps |
| 10% | 90.00 Mbps |
| 15% | 85.00 Mbps |
| 25% | 75.00 Mbps |
Effective Bandwidth = 100 Mbps × (1 − overhead %); actual overhead depends on the specific VPN protocol and configuration in use.
How to Use This Calculator
- Enter the Raw Bandwidth (Mbps) of your underlying connection.
- Enter the VPN Overhead (%) — typically 5–15%, defaults to 10%.
- Select Calculate to get the estimated effective bandwidth through the VPN.
Related Calculations
If the VPN traffic needs to fit within a specific subnet, check the Firewall Rule Calculator, or estimate authentication overhead separately with the Two-Factor Authentication Time Calculator.