Is my broadband slow? A 5-minute diagnostic

Step 1: Decide what “slow” actually means for you

“Slow” is a feeling. Before you can fix it, you need a number. The fastest way to do that is to compare three things: the plan you’re paying for, the speed you actually get, and the speed you need.

If your wired speed test result clears the row you fall into, your broadband isn’t slow — the discomfort is somewhere else (Wi-Fi, a specific app, or a single device hogging the line).

Step 2: Take Wi-Fi out of the equation

The single most common diagnostic mistake is testing broadband over Wi-Fi. A 1 Gbps fibre plan can easily read 80 Mbps over a weak 2.4 GHz signal in the back bedroom — that’s a Wi-Fi result, not a broadband result.

Plug a laptop directly into your router with an Ethernet cable. Close every other tab and app. Then run the test. That number is what your line is actually delivering.

Step 3: Identify which of the four bottlenecks is yours

Slow broadband, as users experience it, almost always falls into one of four categories. Match your symptoms to the right one and the fix becomes obvious.

Bottleneck 1: The line itself

Symptom: wired Ethernet speed test reads well under your plan, all hours of the day.
Likely cause: your ISP is under-delivering, the line into your home is degraded (especially DSL), or you’re on an older technology than you realise.

What to do: screenshot three wired tests at different times of day and contact your ISP with them. UK customers can quote Ofcom’s Voluntary Code of Practice on speeds; US customers can reference their plan’s “typical” speeds from the Broadband Facts label. If the line is genuinely degraded, ask for a line test or an engineer visit.

Bottleneck 2: The router

Symptom: wired test is fine, but Wi-Fi is much slower in every room.
Likely cause: aging router, weak antennas, on an old Wi-Fi standard (anything before Wi-Fi 5 / 802.11ac), or running too many devices on 2.4 GHz.

What to do: if your router is the one your ISP shipped four+ years ago, replacing it is the highest-leverage upgrade you can make. A modern Wi-Fi 6 or 6E router will often double real-world household speeds without changing your plan. Place it centrally, off the floor, away from microwaves and metal.

Bottleneck 3: Wi-Fi conditions

Symptom: fine speeds near the router, much slower one floor or one room away.
Likely cause: walls, interference, distance, neighbour’s networks stomping on the same channel.

What to do: move the router, switch to 5 GHz for nearby devices, or add a mesh node (Eero, Deco, Orbi, Plume) for far rooms. Mesh nearly always beats a single high-end router for whole-home coverage.

Bottleneck 4: A single device

Symptom: one phone, laptop or TV feels slow; everything else is fine.
Likely cause: old Wi-Fi chip, background sync, malware, or a misconfigured DNS.

What to do: run a speed test on a second device side-by-side. If the problem follows the device, restart it, check what’s running in the background, and try changing DNS to 1.1.1.1 or 8.8.8.8.

Step 4: Re-test at different times

Broadband isn’t a constant. Cable and DSL share capacity with your neighbourhood, so peak-time speeds (7pm–11pm) commonly drop 20–40% on congested ISPs. If your morning test is 300 Mbps and your evening test is 90 Mbps, it’s not your gear — it’s your provider’s local capacity.

Run the test at three points: mid-morning, early evening, and late at night. Save the results. If only the evening one is weak, you have a contention problem, which is a legitimate basis for a complaint or a switch to fibre-to-the-premises if it’s available.

Step 5: Know when to actually switch

Switch ISPs when, in this order: 1) your wired peak-time speed is consistently under 70% of your plan, 2) your ISP has refused or failed to fix it after a formal complaint, and 3) a faster technology (fibre-to-the-premises, fixed wireless 5G, or a different cable provider) is available at your address.

Don’t switch over a single bad test, a Wi-Fi problem you haven’t fixed, or a router issue. You’ll churn through providers and the underlying problem will follow you.

Common questions

What broadband speed is considered slow in 2026?

The UK’s Ofcom and the US’s FCC both define broadband as a minimum of 25 Mbps download and 3 Mbps upload. Anything below that on a wired test is genuinely slow. For modern households doing 4K streaming and video calls, the practical floor is closer to 100 Mbps down.

Why is my broadband slow only at night?

Peak-time congestion. Cable and DSL networks share local capacity, so evening traffic (7pm–11pm) routinely outstrips daytime capacity. Fibre-to-the-premises is much less affected. Detailed write-up: why your broadband speed test results vary.

How do I know if it’s my Wi-Fi or my ISP?

Plug a laptop into the router with Ethernet. If the wired test matches your plan, Wi-Fi is the problem. If both are slow, it’s the line or your ISP.

Is 100 Mbps slow?

For a 2–3 person household with 4K streaming and video calls, 100 Mbps is comfortable. It only starts feeling slow with four or more heavy users at once, or with constant large cloud backups. See what is a good broadband speed in 2026.

Can broadband get slower over time?

Yes — usually because your ISP oversells local capacity as more neighbours join, your router ages, or a copper line degrades. Fibre lines themselves don’t slow with age.