What your result actually means
Download speed is the rate data reaches you, measured in megabits per second (Mbps). It is the figure almost every broadband package is sold on, and the one that governs streaming, browsing and downloads.
Upload speed is the rate data leaves you. It matters more than most people expect: video calls, cloud backups, sending large files and streaming to an audience all lean on it. On full fibre it is often a third of your download speed or better. On older copper-based lines it can be a twentieth of it.
Ping, also called latency, is how long a packet of data takes to reach a server and come back, measured in milliseconds. Ofcom's guidance is that most online activity needs latency under 100ms, and some online gaming benefits from under 50ms. A connection can have a high download speed and still feel sluggish if ping is poor.
Jitter is the variation in that delay from one packet to the next. Steady latency matters more than low latency for calls and video. High jitter is what makes a voice call break up even when your speed test looks healthy.
Packet loss is data that never arrives at all. Small amounts are normal and get corrected automatically. Persistent loss points at a fault rather than a slow package.
Megabits and megabytes are not the same thing
Speeds are quoted in megabits (Mbps). File sizes are quoted in megabytes (MB). There are eight megabits in a megabyte, so a 100 Mbps connection downloads roughly 12.5 MB each second at full tilt.
That gap catches a lot of people out. A 2 GB game update on a 100 Mbps line takes around two and a half minutes, not twenty seconds. If your downloads feel slower than your speed test suggests they should, this is usually why.
Why the number changes every time you test
Run the test twice in a row and you will often get two different numbers. That is normal, and it is the single most common reason people distrust speed tests. Here is what moves the figure.
Wifi, more than anything else. When Ofcom ran its own national broadband measurement programme, it measured only as far as the router and never over wifi, because wifi performance sits outside what a provider can control or guarantee. Your result over wifi is a test of your home network as much as your broadband line.
Your own hardware can be the ceiling. Ofcom's measurement units connected to routers over Gigabit Ethernet, which carries data at 1 Gbit/s but tops out around 940 Mbps once packet overhead is accounted for. That limit meant Ofcom could not measure Virgin Media's 1.13 Gbit/s package with its standard equipment at all. If you are on a gigabit package, your router's ethernet port, your laptop's network card or your wifi chip can all cap the result before your broadband line does.
The time of day. Peak time is formally defined as 8pm to 10pm, in both Ofcom's code of practice and the UK advertising rules. In Ofcom's final round of measurements, older copper-based lines averaged around 92% of their maximum speed at peak, while full fibre held up at closer to 97%.
Everything else using the connection. A phone backing up photos, a console downloading an update or someone else on a video call will all take a bite out of your result.
The test itself. Different speed tests use different servers, different amounts of test data and different numbers of simultaneous connections, so they legitimately produce different numbers on the same line at the same moment.
The practical answer is to treat one result as a snapshot rather than a verdict. Test with a cable if you can, close other apps, and run it a few times across different parts of the day before drawing any conclusion. If you want to build a case with your provider, test at peak time and write down the date, time and figure each time.
Are you getting the speed you pay for?
There are two different numbers attached to your package, and only one of them carries any rights.
The advertised speed is a marketing figure. Since May 2018, any speed quoted in a UK broadband advert has had to be achievable by at least half of that provider's customers at peak time, and has had to be described as an average. Before that rule, an advertised speed only had to reach 10% of customers, which is why older "up to" claims felt so detached from reality. It is a far better figure than it used to be, but it is still a description of the customer base, not a promise to you.
The minimum guaranteed speed is the one that matters. If your provider has signed Ofcom's Voluntary Code of Practice on Broadband Speeds, it had to give you this figure before you bought. On cable and full fibre, it must be at least half the advertised speed. On copper-based lines, it is based on the slowest tenth of comparable lines, adjusted for congestion.
So a 500 Mbps full fibre package carries a guaranteed floor of at least 250 Mbps. You will find your own figure in your original contract paperwork or your online account. If your wired result at peak time is consistently below it, you have something to act on.
What you can do if you are falling short
Report it to your provider first. From the day you report the problem, a provider that has signed the code has 30 calendar days to fix it. They may send an engineer to check the line or replace your router.
Two things then have to be true. Your speed has to stay below your minimum guaranteed figure on at least three successive days after you reported it, and the problem has to be unresolved 30 days on. At that point the provider has to let you leave without an early termination fee. That right covers the whole bundle, so any TV or phone service bought alongside the broadband goes with it, and it applies at any point in your contract rather than only at renewal.
Nine providers have signed the residential code: BT, EE, NOW Broadband, Plusnet, Sky, TalkTalk, Utility Warehouse, Virgin Media and Zen Internet. Vodafone has not signed it. This is a voluntary commitment rather than a legal right, so it binds the providers on that list and no others. If yours is not among them, check what its own contract terms promise.
Slow is not the same as down
These two get mixed up constantly, and they lead to completely different outcomes.
Ofcom's automatic compensation scheme pays out for a total loss of service, a missed engineer appointment or a delayed installation. It does not cover a connection that works but runs slowly. A chronically slow line gets you the right to leave without penalty, not a payment. Plenty of pages online blur the two, so it is worth being clear which situation you are actually in before you contact your provider.
If you are on 4G or 5G home broadband
Almost every piece of speed-test advice online assumes a fixed line, down to suggestions about master sockets and cable condition. Mobile home broadband behaves differently.
Your speed depends on how far you are from the mast, how many other people are using it, and where the router sits in your home. Moving the router to a different window can change your result more than any tweak would on a fixed line. Expect wider swings through the day than a fibre line would show, because you are sharing capacity with mobile traffic.
Ofcom's 2022 revision of the code widened it to cover all access technologies, so a signatory selling you mobile home broadband should still give you a minimum guaranteed speed. It is worth asking what yours is, because the figure is far less predictable than it is on a fixed line.
Before you switch to fix a slow line
If your line is broken, a more expensive package will not repair it. A 60 Mbps connection delivering 10 Mbps has a fault, and paying for a faster tier on the same technology usually inherits the same problem.
Switching genuinely helps when the technology itself is the limit. Moving from a copper-based connection to full fibre changes what is physically possible on your line, and so does moving to a provider whose network actually reaches your address. Our area guides show which networks have built where, and and our broadband hub is the place to start if you are weighing up a move before you commit to anything.
