Why your office Wi-Fi crawls by late afternoon

The pattern is recognisable: mornings are fine, and from mid-afternoon video calls break up, file uploads crawl, and somebody eventually suggests increasing the subscription bandwidth.

That is almost always the wrong fix, because it is almost always the wrong diagnosis. This article lets you describe the problem accurately — to a vendor or to your IT team — and rule out false leads before spending anything.

Bandwidth is almost never the cause

Two things everyday language conflates need separating.

Subscription bandwidth is what enters the building. It is the number the operator sells.

Local network capacity is what travels between your devices and the access points. That is shared space: when fifteen people are on it, nobody gets all of it.

The test that settles it in two minutes: plug a computer into the network with a cable and rerun a speed test at the moment everyone is complaining. If the result is fine on cable and poor on Wi-Fi, the subscription is not the problem, and increasing bandwidth will change nothing.

Cause 1 — too many devices per access point

A Wi-Fi access point talks to one device at a time. It switches between them very quickly, which creates the illusion of simultaneity, but airtime is shared: the more active devices, the less each one gets.

The real count often surprises. Every person brings a laptop and a phone, sometimes a tablet; add printers, cameras, meeting-room displays and the connected objects nobody inventories. A room of twenty people routinely reaches fifty devices.

An idle device consumes little, but it does consume: it checks in regularly. So the first useful step is to count what is connected, in your access point's or router's interface, and note the gap with what you imagined.

Cause 2 — saturated channels

Wi-Fi uses two frequency bands, and they do not behave the same way.

The 2.4 GHz band travels far and passes through walls well, but it is narrow: only a few channels, shared with all your neighbours as well as microwaves and various wireless equipment. In an office building it is often unusable during the day for that reason alone.

The 5 GHz band travels less far and passes through walls less well, but it offers many more channels — hence far fewer neighbours on yours.

Observing this is free: a Wi-Fi analysis app, available on any phone, shows the surrounding networks and each one's channel. If ten networks sit on the same 2.4 GHz channel as yours, you have part of the explanation.

Two fixes, with no purchase: manually pick a less crowded channel rather than leaving automatic selection on, and check that your recent devices are actually using 5 GHz. Many stay stuck on 2.4 GHz because both bands share the same network name and the signal looks stronger there.

Cause 3 — placement

An access point installed where the network socket happened to be, six years ago, is not a choice: it is an accident that lasted.

Three rules suffice. An access point goes high and in the open, not in a comms cupboard or behind a metal panel — metal and water stop the signal, and human bodies are mostly water. It goes at the centre of the area to cover, not at one end, otherwise half its range goes into the car park. And two access points too close on the same channel interfere with each other: adding hardware without thinking about placement sometimes makes things worse.

The check is empirical and reliable: walk the offices with a phone watching the signal indicator, in the places where people actually work. Weak zones show up in ten minutes, and they rarely match what was assumed.

Cause 4 — everyone on one network

A single network for workstations, personal phones, visitors, cameras and connected objects creates two problems at once.

The first is security: a visitor's phone ends up on the same network as your file servers.

The second is performance, and it gets forgotten: a device downloading a multi-gigabyte update consumes airtime the others no longer have. Separating a guest network — a feature present on practically all professional equipment — lets you give it lower priority, and puts personal use out of the way of work use.

What can be fixed with no budget

Action	Cost	Expected effect
Pick a less crowded channel	None	Immediate where neighbours saturate the band
Move recent devices to 5 GHz	None	Clear in dense environments
Move and clear an access point	None or low	Strong on poorly covered zones
Create a separate guest network	None	Moderate, plus a security gain
Put desktops on cable	Low	Frees airtime for mobile devices
Add an access point	Real	Only after the five rows above

The order matters. Buying hardware before the diagnosis sometimes amounts to adding a source of interference to a network already suffering from interference.

If slowness follows the time of day, look at saturation. If it follows where you are standing, look at placement. Both can be observed for free, in half an hour.

When infrastructure work is genuinely needed

Three situations justify investment: an area too large to cover with one or two access points, a number of simultaneous devices that durably exceeds what consumer equipment holds, and a need for continuity — constant video calls, production terminals, telephony over the network — where interruption has a direct cost.

In those cases what changes is not the power of the access points but their number, their distribution and their coordinated management. That is the subject of our Network & Connectivity page. If the diagnosis is unclear, describe the symptom to us — the hour, the place, the number of people: that is what allows an answer without a site visit.