Why is my WiFi slow at night?

Evening slowdown has three distinct causes, and they are frequently confused because the symptom is identical: everything gets slower after about 8pm. The diagnosis matters, because only one of them is the provider's problem.

The three causes are neighbourhood WiFi congestion, provider network contention at peak time, and your own household using more bandwidth in the evening. Test with a cable at 8pm: if the wired speed holds up, the problem is WiFi congestion in your home or street. If the wired speed also drops, it is provider contention or your own usage.

Cause one: neighbourhood congestion

WiFi runs on unlicensed spectrum shared with every other router within range. In a dense street or a block of flats, twenty networks competing for the same channels produce interference that no provider can fix, and it is worse in the evening because that is when everyone is home.

The tell is that the wired speed is unaffected while WiFi degrades, and that the degradation is worse in rooms facing other buildings.

• Switch to the 5 GHz band if your devices support it. It has less range but far more capacity and much less interference.
• Change the channel on 2.4 GHz — most routers default to a crowded one. A WiFi analyser app will show you which channels are free.
• Move the router away from the wall shared with a neighbour if you can.

Cause two: provider contention

Fixed networks are shared, and the sharing ratio is designed around expected peak usage. When a street or a segment fills up in the evening, individual speeds drop. This is normal engineering, not a fault, provided it stays within the range the provider promised.

The tell is that the wired speed drops in the evening and recovers by midnight — and that it has always done so rather than starting suddenly.

This is the one case where a faster package may genuinely help, because higher tiers are usually provisioned with more headroom. But check the wired speed first: if it is close to what you pay for even at 8pm, the provider is delivering and the bottleneck is elsewhere.

Cause three: your own household

The least mysterious explanation is often correct. In the evening, several devices stream at once, someone is on a video call, a console downloads an update, and a phone backs up photos. A 60 Mbps line shared five ways at 4K resolution is saturated.

The tell is that a single-device test at 8pm performs well while everything slows down when the household is active.

• Put the TV and console on a cable. This removes the two heaviest consumers from the WiFi.
• Schedule large downloads and cloud backups for overnight.
• Check the router's admin page for what is actually connected — an unexpected device is sometimes the answer.

The ten-minute diagnosis

Run a wired speed test at 8pm on a weekday, then the same test over WiFi in the room where it feels worst, then again at 11pm. Three results separate the causes cleanly: wired fast and WiFi slow points to congestion in the air; wired slow at 8pm and fast at 11pm points to the provider; both consistent but slow when the household is busy points to your own usage.