Does a VPN slow down your internet?

Yes, a little, nearly always. A VPN adds a round trip to a server that is not on your direct path, and every packet has to be encrypted on your phone and decrypted at the far end. With a nearby, lightly loaded server and a modern protocol the cost is typically a few milliseconds of latency and a small share of throughput, which most apps never show you. With a distant or busy server, or on a network that forces the app onto a slower transport, the cost can be large enough to notice.

Where the slowdown actually comes from

Four things add up, and they are not equal.

Distance. Your traffic goes from your phone to the VPN server and only then to the website, so it travels further than it would have. Light in fibre covers roughly 100 km per millisecond, so each 100 km between you and the server adds about 1 ms in each direction before any routing detours. A server 300 km away adds a few milliseconds of round-trip time; a server on another continent can add 100 ms or more.

Server load. A VPN server has a fixed uplink, a fixed amount of processor time and a limit on how many sessions it can carry well. When it is near any of those limits, your share shrinks. Load often matters more than distance, which is covered in what server load is.

Protocol. Encrypting traffic costs processor time. WireGuard was designed to keep that cost low and has a small per-packet overhead, so on a phone it is close to free. Older protocols do more work per packet. A TLS-wrapped transport on TCP port 443, which a VPN app uses when a network blocks UDP, is slower again: it runs TCP inside TCP, so two layers of congestion control fight each other whenever a packet is lost, and it has to use a smaller packet size (an MTU of 1280 bytes) to fit inside the wrapper.

Your own network. A VPN cannot make a weak Wi-Fi signal or a congested cell tower faster. It adds its cost on top of whatever the network already gives you. If the connection is slow with the VPN off, it will be at least as slow with it on.

How much is typical

There is no single number, and anyone who quotes one without saying which server and which network is guessing. As rough guidance:

Whether you notice depends on what you are doing. Browsing and messaging are limited by latency to the site, not by raw throughput, and a few milliseconds is invisible. A large download shows lost throughput plainly. A video call or a game shows added latency and jitter first. The latency versus bandwidth explainer goes through which one each activity cares about.

When a VPN seems faster

Occasionally a VPN makes a connection quicker. The usual reason is routing: the path from your carrier to a particular site may take a poor peering route, while the VPN server sits on a network with a more direct one. It happens, and it is real when it does, but it is not something a VPN can promise. If you see it, it is a property of that server and that destination on that day.

How to tell what is slowing you down

Measure with the VPN off first, so you know what the network itself gives you. Then look at the app's latency figure for the city you are connected to. If the city shows a low round trip and the connection is still slow, the server is probably busy or the network is forcing a slower transport. If the round trip itself is high, the server is far away or the route to it is poor, and a different city will help more than anything else. Why your VPN is slow works through the fixes in order.

Culvert VPN measures a real round trip from your phone to each city, ranks servers by load and distance, and connects you to the healthiest server in the city you tap, using WireGuard whenever the network allows it; it is free on Google Play.