Why Is My Wi-Fi Slow at Night? (And Slow on One Phone but Not the Laptop)

All day the connection is fine. Then around eight in the evening the video starts buffering, the game lags, and the speed test shows a third of what you pay for. Nothing in your flat changed. What changed is that everyone else’s evening started too.

Why does Wi-Fi slow down at night?

Because Wi-Fi is shared, twice over, and the evening is when everyone shows up to share it.

Shared air. Wi-Fi is radio. Your router and every router in range are talking on the same handful of channels, and radio only lets one device transmit on a channel at a time. Before a device sends, it listens; if the channel is busy, it waits a random few microseconds and listens again. That’s the protocol (CSMA/CA, if you want the name), and it’s polite to a fault. At 2 pm, with the neighbours out, your router gets most of the airtime. At 9 pm, with eleven networks streaming Netflix through the same walls, it gets its turn in a queue.

Shared cable. The line from your home to the internet isn’t yours alone either. On cable broadband (DOCSIS), a few hundred homes share one segment back to the provider’s node. On fibre (GPON), a splitter feeds 32 or 64 homes from one strand. The provider sizes the segment assuming not everyone uses it at once, which is true at 3 am and false at 9 pm. That’s contention, and it’s why the advertised “up to” speed is a daytime number.

The first one is in your building. The second is in your street. The fixes are different, so it’s worth telling them apart.

Is it my Wi-Fi or my internet?

Run a speed test twice: once on Wi-Fi, once with a laptop plugged into the router by Ethernet cable. If the cable is fast and the Wi-Fi is slow, the problem is the air. If both are slow, the problem is the line, and the fix is a phone call or a different provider.

If Speedtest says fast but Netflix is slow, that’s a third thing: the test measures a path to a nearby server; the video comes from wherever the content lives. Congestion at the handover between your ISP and the content network shows up only on real traffic. There’s not much you can do about that one except complain, or use a different service.

Why is Wi-Fi slow on my phone but not the laptop?

Nearly always one of these:

The phone is on 2.4 GHz and the laptop is on 5 GHz. Most routers broadcast both bands. 2.4 GHz travels further through walls but has only three non-overlapping channels (1, 6 and 11), and every microwave oven, baby monitor and neighbour is on them. 5 GHz has around twenty channels, is much less crowded and is far faster, but has shorter range. A phone that’s been handed to the 2.4 GHz band because it drifted out of 5 GHz range will crawl. Check which network name the phone is on; if your router lets you name the bands separately, join the 5 GHz one.

One slow device slows everyone. Airtime is shared by time, not by data. A device with a weak signal talks at a low data rate, so sending the same file takes it longer, and while it talks nobody else can. An old smart plug in the garage, limping along at 1 Mbps, can eat a surprising slice of the evening.

The phone is doing something in the background. Photo backup and app updates default to “when on Wi-Fi and charging”, which describes 10 pm precisely.

Why is my upload speed slow?

Because almost every home connection is asymmetric by design. Cable and ADSL give most of the capacity to download because that’s what most people do most of the time. A 200 Mbps down line is often 10 to 20 Mbps up. Video calls, cloud backups and a teenager streaming to Twitch all fight over that smaller pipe, and it saturates first. If upload matters to you, fibre is the fix; it’s usually symmetric.

What actually helps?

1. Move to 5 GHz for anything that can reach it. Name the bands separately so you can choose.
2. Change the 2.4 GHz channel to 1, 6 or 11, whichever your router’s scan shows is least used. “Auto” often picks badly.
3. Put the router in the open, high up, near the middle of the home. Not in a cupboard, not behind the TV, not next to the microwave.
4. Cable what doesn’t move. A TV or a desktop on Ethernet is one less talker in the air, and it frees airtime for the things that can’t be cabled.
5. Turn on QoS if the router has it, so a video call wins over a background download.
6. Retire the slowest device or give it its own old router, so it stops holding the floor.

None of this adds capacity to the street. But most “slow at night” complaints are the air, not the cable, and the air is yours to fix.

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Topics: wifi slow · why is my wifi slow at night · wifi slow on phone but not other devices · wifi slow iphone · wifi slow on laptop · speedtest fast but internet slow · wifi slow upload speed · 2.4 ghz vs 5 ghz