The short answer
Test at 9pm with a cable straight into your router. If the wired result is fine and Wi-Fi is not, your neighbours’ Wi-Fi is congesting your channel — change it. If wired is also slow at 9pm but fast at 11am, the congestion is your provider’s and only they can fix it.
Evening buffering is the single most reported internet complaint, and it has exactly two causes. The wired test separates them in five minutes and determines whether you are changing a setting or making a phone call.
Cause one: Wi-Fi channel congestion
In flats and terraced housing, dozens of networks share the same few channels. The 2.4 GHz band has only three that do not overlap. At 8pm everyone is home and streaming, the shared airtime runs out, and your connection stalls even though your internet service is delivering exactly what you pay for.
The signature is that a wired device is fine while Wi-Fi struggles at the same moment.
What to do
- Set the 2.4 GHz channel to a fixed 1, 6 or 11 rather than Auto, choosing whichever is least used nearby.
- Move everything capable onto 5 GHz, which is far less crowded and usually resolves the problem outright.
- Split the bands into separate network names so devices stop being steered around.
- Move the router away from other electronics, and out of any cupboard.
Cause two: your provider’s congestion
If the wired test is also slow in the evening, the contention is upstream — too many customers sharing capacity at peak times. Nothing inside your house changes this.
What helps is evidence. Run speed tests at several times of day over a week, wired, and record the results. A clear pattern of full speed at 11am and a fraction of it at 9pm is exactly what a provider needs to escalate a contention problem, and it moves the conversation past the standard script.
Test wired at peak time
Plug a laptop directly into the router with Ethernet at around 9pm and run a speed test. This is the decisive measurement.
Test the same way at a quiet time
Mid-morning, same cable, same laptop. Compare.
Interpret the two results
Wired fine at peak, Wi-Fi poor: your Wi-Fi channel. Wired poor at peak, fine off-peak: your provider. Both poor at all times: a line fault, which is also your provider’s.
Fix the channel if it is your Wi-Fi
Fixed 2.4 GHz channel, devices on 5 GHz, bands split, router in the open.
Collect a week of evidence if it is upstream
Wired tests at several times daily, written down with timestamps. Then contact your provider with the pattern rather than a single bad result.
Cloud photo backups, game updates, security camera uploads and another person’s video call all consume the same connection. Uploads hurt most, because upload capacity is usually a fraction of download. Scheduling backups overnight is free and occasionally solves the whole problem.
Frequently asked questions
Why is my internet slow only at night?
Either your Wi-Fi channel is congested by neighbours, or your provider’s local capacity is oversubscribed at peak. The wired test at peak time tells you which.
Will a new router fix evening slowdowns?
Only if the cause is your Wi-Fi. A new router cannot create capacity on your provider’s network, which is why people who upgrade for this reason are often disappointed.
What does contention ratio mean?
How many customers share the same capacity. A higher ratio costs less and degrades more at peak times. Providers rarely publish it, which is why your own measurements matter.
Does using a VPN help with evening throttling?
Only in the specific case where a provider is throttling particular services rather than being short of capacity. Against genuine congestion a VPN adds a hop and usually makes things slightly worse.
Do the wired test at 9pm. It costs five minutes and decides whether this is a setting you can change or a call you need to make.
