Your speed test says 300 Mbps and the internet still feels broken — here is why

You are not imagining it, and the speed test is not lying to you. It is answering a different question from the one you asked.

A speed test measures how much data you can pull in a short burst. Almost nothing that makes a connection feel broken is a bursting problem. Video calls that freeze, pages that hang before loading instantly, games that rubber-band on a 900 Mbps line — all of those are failures of timing and reliability, and a speed test measures neither.

Below is a table that maps what you are actually seeing onto the thing that is actually failing. If you read nothing else, read that.

What a speed test measures — and what it ignores

It measures peak download and upload throughput, in a burst of a few seconds, to a nearby server, usually while the rest of the house is quiet. That is close to a best case by design.

It ignores latency under load, jitter, packet loss, DNS lookup time, how your Wi-Fi behaves over minutes rather than seconds, how the line performs at 8pm, and everything that happens beyond your provider’s network.

A speed test is a sprint time. It tells you nothing about whether the road is potholed, whether it is closed at rush hour, or whether your car stalls at every junction.

Which one is it? Match your symptom

What you’re seeing	What’s actually failing	Usual cause	Where to go next
Everything crawls the moment someone starts a download	Latency under load	Bufferbloat	Bufferbloat, below
Video calls freeze for 30–60 seconds, then recover	Jitter or packet loss	Wi-Fi, or an unstable line	Fix slow Wi-Fi · jitter
Games rubber-band on a fast line	Packet loss	Line quality, or the route to the server	Reduce ping for gaming · good ping
Pages hang, then load all at once	DNS	Slow or failing resolver	DNS, below
Fast downstairs, unusable upstairs	Wi-Fi coverage	Placement, walls, band	Fix slow Wi-Fi · extender vs mesh
Fine all day, awful from 8pm	Congestion, or a scheduled task	Contention, backups, updates	Internet slow at night
Streaming buffers but the speed test is perfect	The service or the route	The app, a CDN, or the far end	Not your connection, below
Ethernet slower than Wi-Fi	Cable, port or adapter	A bad lead, or a 100 Mbps port	Wired vs Wi-Fi
Everything is slow only on a work laptop	VPN	The VPN route, or its server	Is a VPN slowing you down?

The six things that break a fast connection

Ranked by how often they turn up in UK support forums — which is what the ranking is, not a measured share. Nobody publishes reliable UK figures for this, so we are not going to invent percentages.

1. Latency under load (bufferbloat)

What it is. Your router, or equipment on your provider’s network, holds on to too much data instead of dropping it. The IETF’s own description, in RFC 8033, is “a phenomenon in which excess buffers in the network cause high latency and latency variation”.

What it feels like. Everything is fine until anything else starts moving data. Someone uploads a video, a cloud backup kicks in, a console starts an update — and suddenly calls break up and pages stall. Ping at rest might be 15 ms; under load it can pass 400 ms.

How to check it. You cannot see this with a normal ping test, because a normal ping test runs on an idle connection. You need a test that measures latency while loading the line — see the next section.

What fixes it. Usually nothing you have to buy. Turn on SQM (Smart Queue Management) or QoS in your router settings if it has them. Setting the queue limits slightly below your actual line speed is what does the work. If your router has neither, that is one of the few cases where new hardware is the honest answer.

2. Jitter

What it is. Variation in latency — the gaps between packets arriving become uneven.

What it feels like. Robotic audio, video that freezes and catches up, calls that recover after a few seconds. Voice and video hate jitter more than they hate a high but steady ping.

How to check it. Most latency tests report it alongside ping. Compare wired with wireless — on most home connections jitter is a Wi-Fi problem.

What fixes it. A cable. Then, if it persists on a cable, it is a line fault worth reporting.

3. Packet loss

What it is. Some data never arrives and has to be sent again.

What it feels like. Stalling rather than slowness. Downloads that pause and resume, a call that drops a word, a game that rubber-bands. Even 1–2% is obvious on a video call, while leaving a speed test looking healthy — the test simply re-sends and still records a high total.

How to check it. A sustained test over at least a minute, wired.

What fixes it. If it only happens on Wi-Fi, it is interference or range. If it happens on a cable, it is a fault: report it, with numbers.

4. DNS

What it is. Before your browser can fetch anything it has to look up the name. That lookup is separate from the download.

What it feels like. The giveaway pattern: pages hang on “looking up…” for several seconds and then load instantly once they start. Your speed test is untouched, because it resolves one name once and then measures the transfer.

How to check it. If a site loads instantly by IP address but slowly by name, it is DNS. Less technically: if everything is slow to start but fast once it starts, suspect DNS.

What fixes it. Changing your DNS resolver, in the router so it applies to the whole house. Free, reversible, and takes two minutes.

5. Wi-Fi, not the line

What it is. You ran the speed test standing next to the router. The laptop that has the problem lives two floors up.

What it feels like. Fine in one room, unusable in another. Or fine on a phone, bad on an older laptop — one old device on an old Wi-Fi standard can drag a whole band down for everyone.

Ofcom puts the principle better than we can: your Wi-Fi connection will never outperform your broadband service. The reverse is what catches people out — your broadband can be perfect and your Wi-Fi still ruin it.

What fixes it. Fix slow Wi-Fi, 2.4 GHz vs 5 GHz, and if it is genuinely a coverage problem, extender vs mesh.

6. Not your connection at all

What it is. The service you are using, a content network, the far end of the call, or a VPN in the middle.

What it feels like. One thing is broken and everything else is fine. The classic is “Netflix buffers but my speed test is perfect” — which is almost always this, not your line.

How to check it. Try a different service doing the same job. If one streaming app stutters and another is flawless, your connection is not the problem.

What fixes it. Often waiting. If a VPN is involved, test with it off — is a VPN slowing your internet down?.

Find out which one it is, in ten minutes

1. Plug into the router with a cable and try to reproduce the problem. This single step splits everything in two: if the symptom disappears, it is Wi-Fi, and you can ignore every line-related section above.
2. Run a latency-under-load test, not an idle ping. See below for which.
3. Watch for a full minute with the connection busy, rather than taking one reading. Intermittent faults do not appear in a three-second sample.
4. Repeat it when the problem is actually happening. A morning test proves nothing about an 8pm problem — see internet slow at night.
5. Test a second device. If only one is affected, the fault is that device, and nothing about the line will fix it.

Which test to use

We do not yet have our own latency-under-load test. Our ping and latency test measures latency at rest, which by definition will look fine on a bufferbloated line. Building a loaded test properly is on our list; until it ships, we would rather point you somewhere honest than pretend.

Two we would use:

• Waveform’s bufferbloat test gives the clearest plain answer — a single A+ to F grade based on how far latency rises under load. Worth knowing: it is built by Waveform, a US networking-equipment retailer, and the page below the test recommends routers it earns Amazon commission on. The test itself is sound and runs in a browser with nothing to install; we would use the grade and ignore the shopping.
• Cloudflare’s speed test reports unloaded latency, latency during download and latency during upload as separate figures, with no commercial content at all. It does not give a bufferbloat grade — it scores your connection for streaming, gaming and video chat — so you read the three latency numbers yourself and compare them.

What a healthy result looks like

Here is the honest position, because it matters more than the numbers.

Ofcom does not publish consumer thresholds for jitter or packet loss. We checked the current speeds code of practice, Ofcom’s consumer advice pages and Connected Nations: the words do not appear with any target attached. For latency, the nearest thing is a research observation from Ofcom’s UK Home Broadband Performance report — most online activities need a response time under 100 ms for a good experience, and some games need under 50 ms — but that came from a research programme Ofcom has since discontinued, and it is not a standard.

The bodies that standardised how to measure these metrics explicitly refused to say what counts as good. RFC 3393, which defines the jitter metric, states in terms: “we specifically do not specify particular values of the metrics that IP networks must meet.”

So the bands below are NetSorted’s own rules of thumb, not standards, not regulated thresholds, and not anybody’s official position. They reflect what a UK home connection generally manages and what tends to be noticeable in use.

Measured wired	Fine	Worth looking at	Something is wrong
Ping at rest	under 30 ms	30–60 ms	over 60 ms
Rise in ping under load	under 30 ms	30–100 ms	over 100 ms
Jitter	under 5 ms	5–20 ms	over 20 ms
Packet loss	0%	under 1%	1% or more

Treat them as a prompt to investigate, not a verdict. A line sitting in the middle column and behaving perfectly is fine.

What to say to your provider

If you have already been told your speed is within your estimate, this is the section you came for. Do not argue about the speed — report the thing that is actually broken.

Copy this, fill in your own figures, and read it out or paste it into chat:

I am reporting a service fault, not a speed fault. My download speed is [X] Mbps, which is within my estimate, so please do not close this as a speed issue. The problem is [latency rising from X ms to Y ms under load / Z% packet loss / jitter of X ms], measured on [date] at [time], over a wired connection with all other devices disconnected. It happens [every evening / whenever anything downloads / constantly]. Please log this as a fault and give me a reference number.

Four things make that stick:

• Say wired, and say the other devices were off. That removes their first two deflections before they make them.
• Give dates and times. Intermittent faults need a pattern, and a provider cannot investigate “sometimes”.
• Ask for a fault reference number explicitly, and write it down.
• Report it even while you keep troubleshooting. For a total loss of service the automatic compensation clock runs from when you report, not from when it broke.

What your rights actually are

This is worth getting right, because the two things are often blurred.

Ofcom’s Broadband Speeds Code of Practice covers download speed, and only download speed. Signatory providers must tell you a minimum guaranteed download speed when you buy. If your actual speed falls below that figure on a daily basis for at least three days running after you report it, and they cannot fix it within 30 calendar days, you can leave without penalty — and you can take any bundled phone or TV with you if you want to. It does not apply on a rolling monthly contract.

Two details that matter. The trigger is the minimum guaranteed speed, not the headline estimate — those are two different numbers you were given at point of sale. And the signatories are BT, EE, NOW Broadband, Plusnet, Sky, TalkTalk, Utility Warehouse, Virgin Media and Zen Internet. Vodafone is not on Ofcom’s list for the residential code.

A latency, jitter or packet-loss fault is not covered by that code at all. Those words appear nowhere in it, so there is no speed-code right to exit over them. The route instead is the ordinary one: your provider’s complaints process, which every provider must operate under Ofcom’s rules, and then alternative dispute resolution if it is unresolved after six weeks — reduced from eight for complaints raised on or after 8 April 2026 — or sooner with a deadlock letter.

How to complain about your broadband covers the process, and the complaint letter generator writes the letter.

When it is worth spending money

For most people reading this, the fix costs nothing — a setting, a cable, or a different DNS server. That is the honest answer and it is most of the time.

Three cases genuinely justify a purchase:

• A router too old to do SQM or QoS, on a line with real, measured bufferbloat. Measure first.
• Genuine Wi-Fi coverage failure — thick walls, a long house, a converted loft. Extender vs mesh and the mesh buying guide.
• An upload ceiling no tuning can fix, where a symmetrical package is the actual answer. What speed do I need?

If you are not in one of those three, do not let anyone sell you a router.

→ Use the ping and latency test