Why Your Gigabit Broadband Is Slower Than Advertised
If your broadband feels slower than the number you are paying for, there are only two possibilities and they lead to completely different places. Either you are measuring a wall, a radio or a busy evening, in which case switching provider would change nothing, or your line genuinely is not delivering what was committed to it, in which case you may be able to leave your contract today at no cost. This guide shows you how to tell which, in three speed tests and about fifteen minutes.
The short version
- 1000 Mbps is physically unreachable over a single standard ethernet port. The real ceiling is 949, or about 937 in typical UK conditions.
- Your speed test reports the lowest ceiling in the chain, not the speed of your line. Most people are measuring their Wi-Fi and blaming their provider.
- The advertised speed gives you no rights at all. The figure that does is your minimum guaranteed download speed, which sits in your contract information and is usually much lower.
- Below the guarantee and unfixed in 30 calendar days? Nine providers must then let you leave with no exit fee, taking any bundled TV or phone with you.
- Vodafone and almost every altnet never signed that code. You still have routes, they are just less prescribed.
Why is my broadband slower than advertised?
Direct answer: because a speed test measures the whole chain from a server to your device, and reports whichever link in that chain is narrowest. The fibre outside your house is very often not the narrow bit.
Before we get anywhere near your rights, we need to settle something that trips up almost everybody, because getting this wrong is why so many complaints go nowhere.
1000 Mbps is not achievable over a standard gigabit ethernet port. It never was, and no provider on earth can deliver it. That is not marketing sleight of hand, it is arithmetic.
Data does not travel down a cable as a smooth stream. It travels in frames, and every frame carries baggage: a preamble to announce itself, an address header, a checksum to prove it arrived intact, and a mandatory silent gap before the next one is allowed to begin. On a standard 1500-byte frame carrying ordinary web traffic, that baggage comes to 78 bytes for every 1460 bytes of your actual data.
The working, so you can check it yourself
Your data in one frame = 1460 bytes
On the wire = 1460 + 20 (TCP) + 20 (IP) + 14 (ethernet) + 4 (checksum) + 8 (preamble) + 12 (gap) = 1538 bytes
Efficiency = 1460 ÷ 1538 = 94.93%
Ceiling = 1000 × 0.9493 = 949 Mbps
Turn on TCP timestamps, which most modern operating systems do by default, and it falls to about 941 Mbps. Add PPPoE encapsulation, which many UK connections use, and you are at roughly 937 Mbps. This is why gigabit packages are advertised at "900 Mbps average" rather than 1000. The providers are being accurate, not modest.
Then the losses really start, because a household almost never tests through a bare ethernet cable.
Where a gigabit actually goes
Megabits per second reaching one device. The first two are fixed physics. The last two are your home, and they are the ones you can change.
The illustrative figures above are typical rather than guaranteed, and the exact drop in the bottom two bars depends entirely on your building. Which is precisely the point: the two bars a provider controls are the two at the top.
Free, no sign-up. Wired if you possibly can, and the next section explains why that matters so much.
What is my broadband actually capable of?
Direct answer: whatever the lowest of three separate ceilings allows. Your speed test reports that lowest number, and most people assume they are measuring the first ceiling when they are actually measuring the second or third.
We call these the Three Ceilings, and getting them straight is the difference between a productive phone call and forty wasted minutes.
The Three Ceilings
Same house, same evening, three limits stacked in front of each other. Only the shortest one is visible to you.
310 is the only number you will ever see. It tells you almost nothing about the fibre outside, which in this example is performing perfectly. Diagnose the ceilings and you find the actual problem. Diagnose the number and you find nothing.
Why is my Wi-Fi so much slower than my wired speed?
Direct answer: because Wi-Fi is half duplex and shared. Only one device can transmit at a time, so everything on the network takes turns, and the slowest device sets the pace while it is talking.
The number your laptop shows when you hover over the Wi-Fi icon is a link rate, not a speed. It is the rate the radio has negotiated for the instant it is transmitting, rather like a speed limit sign on an empty road. Real throughput is roughly two thirds of it at best. A common 2x2 device on an 80 MHz channel will report a link rate of 1200 Mbps and deliver somewhere around 800 to 900 Mbps sitting next to the router in ideal conditions, considerably less through a wall (Cisco, n.d.).
Then the queue forms. Because airtime is shared, throughput divides between everything using the channel. One device running a test might see 200 Mbps. Two devices testing at once see roughly 100 each. Four see around 50. Worse, a single ageing device chattering away at a low data rate holds the channel open while it does so, and drags everybody down with it.
| Connection to your device | Realistic ceiling | What limits it |
|---|---|---|
| Gigabit ethernet cable | 937 to 949 Mbps | Frame overhead. A hard physical limit that nothing will improve. |
| 100 Mbps ethernet port common on older laptops | about 95 Mbps | The port itself. Worth checking before you blame anybody. |
| Wi-Fi, beside the router | roughly 800 to 900 Mbps | Radio overhead, and only in ideal conditions. |
| Wi-Fi, through a wall or two | often 150 to 400 Mbps | Distance and obstruction, which fall away sharply. |
| 2.4 GHz Wi-Fi | usually under 100 Mbps | Narrow channels and heavy congestion from every neighbour. |
| Powerline adapter | a fraction of its box rating | Household wiring, which was never designed to carry data. |
So if your phone reports 280 Mbps from the sofa on a gigabit package, nothing has gone wrong. You have measured the sofa. Our broadband speed calculator works out what your household genuinely needs, and our download time calculator converts abstract megabits into the only unit anyone actually cares about, which is minutes.
How do I find out what is really slowing me down?
Direct answer: run three speed tests in one session and subtract. The diagnosis is in the gaps between them, not in any single number.
Do all three between 8pm and 10pm. That window is not arbitrary: it is the peak period Ofcom uses for residential speed estimates, and the same window the Advertising Standards Authority applies to advertised averages (Ofcom, 2022a). Testing at eleven on a Tuesday morning produces a flattering number that nobody will accept as evidence.
The subtraction method
Three tests, two subtractions, one answer. Worked example below.
Verdict in this example: test 1 was healthy, so nothing here is the provider's fault and no exit right applies. Every pound spent switching would have bought the same walls.
Reading your own three numbers
| What you see | The verdict | Your next move |
|---|---|---|
| Wired test healthy, Wi-Fi tests poor | Your home network | Router placement, the 5 GHz band, or a mesh system. Switching would not fix it and you would carry the problem with you. |
| Wired test below your minimum guaranteed speed | Potentially their fault | This is the one that matters. Report it, start the 30-day clock, and read the next section closely. |
| Fine in the afternoon, poor at 9pm, every night | Congestion | Gather dated evidence across several evenings before you ring. One bad night proves nothing. |
| Speed looks fine but calls and games stutter | Not a speed problem | Latency, jitter or bufferbloat. Our live quality monitor sees what a speed test cannot. |
| Drops out completely, then returns | A fault, not slowness | Different rules, and possibly money owed. Try our compensation calculator. |
One test proves nothing
A thirty-second speed test captures thirty seconds. If your complaint is that the connection is unreliable rather than uniformly slow, you need a record across several evenings, which is exactly what our live quality monitor is built to produce. Providers take dated, repeated evidence seriously. They do not take "it feels slow" seriously, and in fairness nor would you in their position.
Adrian's take
I have lost count of the pages that list twenty reasons your broadband might be slow and never once mention that you might be entitled to walk away from the contract. It is the single most valuable thing a reader could learn and it is almost never there. My suspicion is that it sits awkwardly next to a page full of affiliate links, because the honest version of this advice sends a good number of people to their existing provider's complaints line rather than to a new deal. So be it. If your Wi-Fi is the problem, we would rather tell you that and keep your trust than sell you a switch that fixes nothing.
Can I cancel my broadband contract if it is too slow?
Direct answer: sometimes, and the test is narrower than most people expect. It hangs on your minimum guaranteed download speed, not the advertised speed, and it applies to nine providers.
There is a genuine route out of a broadband contract with no early termination charge when a provider cannot deliver the speed it committed to. It exists, it works, and it is one of the least-used consumer rights in UK telecoms, largely because people aim at the wrong number.
Three speed figures, and only one of them gives you rights
| The figure | What it actually is | Gives you a way out? |
|---|---|---|
| Advertised average speed "Average 900 Mbps" | A marketing figure. Advertising rules require it to be achievable by at least half of that provider's customers during the 8pm to 10pm peak. It describes their customer base, not your line. | No |
| Personalised speed estimate "You should get 500 to 700" | A range for your specific address, given at the point of sale. Useful, and a fair basis for a conversation, but an estimate. | Not on its own |
| Minimum guaranteed download speed "Minimum guaranteed 300 Mbps" | The floor, based on the capability of the line into your property. It sits in your order confirmation or contract information document, and it is usually far below the advertised figure. | Yes. This is the one. |
Ringing up to complain that you are not getting the advertised 900 Mbps invites a polite explanation of what "average" means, and you will lose that exchange. Ringing up to say your wired peak-time speed is below the minimum guaranteed figure in your contract is a completely different conversation, because that figure is a commitment rather than a description.
Go and find yours before you do anything else. It will be in your order confirmation email, your contract summary, or the account area of your provider's website. Ofcom requires providers to give you this information without you having to ask, and to remind you of it once your service goes live, so it is there somewhere (Ofcom, 2022a).
How the 30-day rule works
The rule in one paragraph
Under Ofcom's voluntary Broadband Speeds Code of Practice, if your download speed falls below your minimum guaranteed speed, you report it, and the provider cannot resolve a problem on its own network within 30 calendar days, it must let you exit your contract without penalty. Thirty calendar days, not thirty working days. The exit also covers services bundled with the broadband, so you are not left able to cancel the internet while still paying for the television.
The route, end to end
The code is voluntary. If they never signed it, you have a different route, set out further down this page.
Wired at the router, other devices paused, between 8pm and 10pm. Wi-Fi results will not carry you.
The clock starts the day you tell them, so the date is the single most important thing to secure.
Diarise day 30 yourself. Plenty of faults do get fixed in that window, which was the point of asking.
Ask them to confirm the waiver in writing before you place an order elsewhere.
Which providers have signed Ofcom's speed code?
Direct answer: nine of them for residential broadband, and the list is a good deal shorter than most people assume.
- BT
- EE
- NOW Broadband
- Plusnet
- Sky
- TalkTalk
- Utility Warehouse
- Virgin Media
- Zen Internet
Everyone else. That includes Vodafone, and, with the single exception of Zen, the entire alternative network sector: Hyperoptic, Community Fibre, YouFibre, Gigaclear, toob, Zzoomm, BeFibre, brsk and the rest.
The separate business code is smaller still, with only three signatories: BT, TalkTalk and Virgin Media.
Both lists verified directly against Ofcom's codes of practice page on 25 July 2026. These are voluntary codes and the lists do change, so check yours before relying on it. If a provider joins, we will update this page.
None of that is an accusation of poor service. Several non-signatories are among the fastest and best-regarded providers in the country, and many publish speed guarantees of their own that are more generous than the code requires. It simply means the specific Ofcom-defined 30-day route is not automatically open to you, so it pays to know which conversation you are having before you pick up the phone.
Does automatic compensation cover slow broadband?
Direct answer: no, not at all. Speed and service failure are governed by two different voluntary codes with two different signatory lists, and confusing them is one of the most common mistakes in UK broadband complaints.
| Provider | Speeds code slow speeds, 30-day exit | Automatic compensation total loss, missed appointments, late starts |
|---|---|---|
| BT, EE, Plusnet, Sky, NOW, TalkTalk, Utility Warehouse, Virgin Media, Zen | Yes | Yes |
| Vodafone | No | Yes |
| Hyperoptic | No | Yes |
| Most other altnets | No | No |
The practical upshot is worth stating twice. Automatic compensation will not pay you a penny for a connection that is merely disappointing. It covers a total loss of service that is not repaired in time, a missed engineer appointment and a delayed start to a new service, paid as bill credit without you having to ask. If you have had any of those, our compensation calculator works out what you are owed, and our guide to compensation for service failure explains the detail. Slow speeds are the speeds code's job. Total failure is compensation's job.
What are the exclusions?
Direct answer: four of them, and knowing them keeps you credible on the phone.
- The problem must be on their network. If your wired speed at the router is fine and the shortfall only appears over Wi-Fi, the code does not help, because nothing has gone wrong with the service they sold you.
- There is a settling-in period after installation. Providers apply a stabilisation window on newly activated lines, commonly around ten days on copper-based connections, while the line finds its stable rate. Speeds during that window do not count.
- Rolling monthly contracts sit outside the process. No great loss, because on a one-month rolling deal you can simply give notice and leave anyway.
- It is a voluntary code, not a statutory right. Ofcom oversees it and signatories are expected to honour it, but it binds only those who signed.
What should I say when I ring my provider?
Direct answer: name the minimum guaranteed speed, say the tests were wired, and ask for the report date in writing. Those three things turn a long call into a short one.
Have three dated wired results in front of you and use something close to this wording.
"I'd like to report a speed fault, please. My minimum guaranteed download speed is [X] Mbps. I've run wired speed tests directly at the router, with other devices paused, at around 9pm on [three dates], and I'm getting [Y] Mbps. Could you log this as a speed fault today and confirm the date in writing? I understand that under the Broadband Speeds Code of Practice you have thirty calendar days to resolve a fault on your network, and that if it isn't resolved I'd have the right to exit without an early termination charge, including the bundled services on this account."
Three things make that work. You have named the correct figure, so nobody can redirect you into a discussion about averages. You have pre-empted the Wi-Fi question by testing wired. And you have asked for the report date in writing, which is what starts the clock and what you will need if this ever reaches an ombudsman.
Then diarise day thirty. Do not rely on them to tell you it has passed.
What if my provider has not signed the code?
Direct answer: you are not without options, they are simply less prescribed. And one route is open to absolutely every UK customer, whatever their provider.
Start with your own contract, because many non-signatories publish their own speed guarantee and some are more generous than the code. Beyond that, the service you were sold still has to be delivered with reasonable care and skill, and the speed information you were given at the point of sale forms part of what you agreed to buy.
Then there is the escalation route, which exists regardless, because Ofcom's general conditions require every UK provider to belong to an approved alternative dispute resolution scheme. Complain formally, in writing. If it is unresolved after six weeks, or sooner if they issue a deadlock letter, take it to the Communications Ombudsman or CISAS, whichever your provider belongs to. That threshold dropped from eight weeks to six in April 2026, which is a genuinely useful change and one of the quieter consumer wins of the year (Ofcom, 2026b).
When is leaving the wrong answer?
Direct answer: whenever the wired test at the router was healthy. In that situation a new provider hands you a new router and the same walls, and you have swapped your contract while keeping your problem.
We compare broadband deals for a living and we would still rather you did not switch for a reason that fixes nothing. Three situations where exiting is the wrong tool.
Move the router off the floor and out of the cupboard, get on the 5 GHz band, and consider mesh in a larger or older house. Our router settings guide covers the free fixes first.
More megabits will not help. A gigabit line with bad bufferbloat feels worse than a 200 Mbps line with good queue management. Our guide to the hidden metrics explains which number to chase.
Plenty of gigabit households would never notice a drop to 500 Mbps, because their real constraint is upload or coverage. Our speed requirements guide takes two minutes, and the honest answer is often that you could pay less.
The fifteen-minute audit
Direct answer: eight steps, and step one is the one everybody skips.
- Find your minimum guaranteed download speed. Order confirmation, contract summary, or the account area. Write it down.
- Check whether your provider is one of the nine. It decides which route you have.
- Test wired at the router, 8pm to 10pm, with other devices paused. Run the test.
- Test on Wi-Fi beside the router, same session, nothing else changed.
- Test on Wi-Fi where you actually sit.
- Subtract. Gap one is Wi-Fi, gap two is your home, and a low first result is your provider.
- Repeat across two more evenings and keep the dates. Three results beat one every time.
- If the wired result is below your guarantee, report it, get the date in writing, and diarise day thirty.
If the exit right does turn out to apply to you, it is worth knowing what you would be exiting to.
The bigger picture
Full fibre now reaches 82% of UK homes and gigabit-capable networks reach 89%, according to Ofcom's Spring 2026 coverage update using data to January 2026 (Ofcom, 2026a). That means the great majority of households could have a connection where the line ceiling is no longer the binding constraint at all, and where the only thing standing between them and a genuinely fast connection is a router in a cupboard.
It is a good problem to have. It is also a slightly awkward one for the industry, because as the line stops being the bottleneck, the gap between what people pay for and what they experience gets harder to explain away. Our broadband speed guide covers what the various tiers actually deliver, and our technology comparison sets out how the connection types differ.
Adrian's closing thought
The most useful sentence in this entire piece is not the arithmetic, satisfying though it is. It is this: go and find your minimum guaranteed download speed. It is in a document you already have, it takes about ninety seconds, and it converts a vague and losable grievance into a specific and winnable one. Most people have never looked at it, and a fair few will be surprised how low it is. Either way you will finish the exercise knowing something concrete about what you are owed, which is more than you knew when you started reading.
Frequently asked questions
Why is my broadband slower than advertised?
Usually because you are measuring something other than your line. A speed test reports the lowest ceiling in the chain, and that chain includes the port or radio between your router and your device, plus whatever the rest of the household is using. A standard gigabit ethernet port caps at about 949 Mbps of usable data, Wi-Fi caps far lower, and evening congestion takes another slice. The advertised speed is also not a promise to you: advertising rules only require it to be achievable by at least half of that provider's customers at peak.
Why does my 1000 Mbps broadband only reach about 940 Mbps?
Because a standard gigabit ethernet port cannot carry 1000 Mbps of usable data. Every frame travels with a preamble, an address header, a checksum and a mandatory gap before the next one. Subtract that overhead and the ceiling is 949 Mbps, dropping to about 941 with TCP timestamps enabled and roughly 937 once PPPoE encapsulation is counted. Your line is not underperforming. The port is full.
Can I cancel my broadband contract if it is too slow?
Sometimes, and the test is narrower than most people expect. Under Ofcom's voluntary Broadband Speeds Code of Practice, if your speed falls below the minimum guaranteed download speed in your contract information, and your provider cannot resolve a problem on its own network within 30 calendar days of you reporting it, it must let you leave with no early termination charge. This applies only to the nine residential signatories, and the trigger is the minimum guaranteed figure rather than the advertised average.
Which UK broadband providers have signed Ofcom's Broadband Speeds Code of Practice?
Ofcom lists nine residential signatories: BT, EE, NOW Broadband, Plusnet, Sky, TalkTalk, Utility Warehouse, Virgin Media and Zen Internet. Vodafone is not a signatory, and neither is any alternative network provider other than Zen. A separate business code has only three signatories: BT, TalkTalk and Virgin Media. Both codes are voluntary, so the lists can change.
What is a minimum guaranteed download speed and where do I find mine?
It is the floor speed your provider commits to when you buy, based on the capability of the line into your property. You will find it in your order confirmation email, your contract summary or contract information document, or the account area of your provider's website. Providers must give you this information without you asking, and remind you once the service is live.
Is the advertised broadband speed a guarantee?
No. Advertising Standards Authority rules require the advertised average to be achievable by at least 50% of that provider's customers during the peak window of 8pm to 10pm. It describes their customer base, not your address, and falling short of it does not by itself give you any right to leave.
Why is my Wi-Fi speed so much lower than my wired speed?
Wi-Fi is half duplex and shared. Only one device transmits at a time, airtime divides between everything connected, and the slowest device holds the channel while it talks. The link rate your device displays is a negotiated ceiling rather than throughput, so expect roughly two thirds of it at best. A 2x2 client on an 80 MHz channel showing a 1200 Mbps link rate typically delivers 800 to 900 Mbps beside the router, and far less through walls.
Does the right to exit cover my TV and phone as well?
Yes, where they are part of the same bundle. Since 21 December 2022 the bundle definition covers any product linked to the broadband financially, contractually or technically, so you should not be left able to cancel the broadband while still tied to the television package you bought alongside it.
Does automatic compensation pay out for slow broadband?
No. Automatic compensation covers a total loss of service that is not repaired in time, a missed engineer appointment and a delayed start to a new service. Slow speeds are not covered. They fall under the separate Broadband Speeds Code of Practice, which has a different and shorter signatory list. Two voluntary codes, two lists, two different problems.
What if my provider blames my Wi-Fi?
Very often they are right, which is exactly why you test wired first. A wired test taken at the router with other devices paused removes the argument entirely. If that result sits below your minimum guaranteed speed, the shortfall cannot be pinned on your Wi-Fi, and the 30-day clock is the right conversation to be having.
Is the 30 days working days or calendar days?
Calendar days, counted from the day you report the problem. Diarise day 30 yourself rather than waiting to be told, because that date is what everything else hangs on.
What can I do if my provider has not signed the speeds code?
Start with your own contract, because many non-signatories publish a speed guarantee of their own. Beyond that the service still has to be delivered with reasonable care and skill, and the escalation route is open to everyone: Ofcom's general conditions require every UK provider to belong to an approved dispute resolution scheme. Complain formally in writing, and if it is unresolved after six weeks, or sooner with a deadlock letter, take it to the Communications Ombudsman or CISAS.
My speed looks fine but everything still feels slow. Why?
Speed is only one of four things that decide how a connection feels. The others are latency, jitter and packet loss, and none of them appear on an ordinary speed test. The most common culprit is bufferbloat, where latency rises sharply the moment the line gets busy, which is why a call stutters as soon as somebody starts a download.
Will switching provider fix my slow Wi-Fi?
No. If your wired test at the router is healthy and only the Wi-Fi results are poor, a new provider hands you a new router and the same walls. Move the router off the floor and out of any cupboard, use the 5 GHz band, and consider a mesh system in a larger or older property before you change contract.
References
- Advertising Standards Authority. (n.d.). Broadband speed claims. ASA. https://www.asa.org.uk
- CEDR. (2026). CISAS: communications dispute resolution. Centre for Effective Dispute Resolution. https://www.cedr.com/consumer/cisas/
- Cisco Systems. (n.d.). 802.11ac wireless throughput testing and validation. Cisco. https://www.cisco.com/c/en/us/support/docs/wireless-mobility/wireless-lan-wlan/212892-802-11ac-wireless-throughput-testing-and.html
- Communications Ombudsman. (2026). Frequently asked questions. Ombudsman Services. https://www.commsombudsman.org/faqs
- Ofcom. (2022a). Broadband speeds: what you need to know. Office of Communications. https://www.ofcom.org.uk/phones-and-broadband/coverage-and-speeds/broadband-speeds-code-practice
- Ofcom. (2022b). Updating and clarifying customers' right to exit contracts for broadband services. Office of Communications. https://www.ofcom.org.uk/phones-and-broadband/service-quality/updating-and-clarifying-customers-right-to-exit-contracts-for-broadband-services
- Ofcom. (2026a). Connected Nations: planned network deployments 2026. Office of Communications. https://www.ofcom.org.uk/phones-and-broadband/coverage-and-speeds/connected-nations-planned-network-deployment/connected-nations-planned-network-deployments-2026
- Ofcom. (2026b). Quicker complaints resolution for telecoms customers under new Ofcom rules. Office of Communications. https://www.ofcom.org.uk/phones-and-broadband/service-quality/quicker-complaints-resolution-for-telecoms-customers-under-new-ofcom-rules
- Ofcom. (2026c). Codes of practice. Office of Communications. https://www.ofcom.org.uk/phones-and-broadband/coverage-and-speeds/codes-of-practice
- Ofcom. (2026d). Automatic compensation: what you need to know. Office of Communications. https://www.ofcom.org.uk/phones-and-broadband/service-quality/automatic-compensation-need-know
- Plusnet. (n.d.). Ofcom voluntary speed code of practice. Plusnet plc. https://www.plus.net/help/legal/ofcom-voluntary-speed-code-of-practice/
Written by Adrian James, Broadband Editor at BroadbandSwitch.uk (LinkedIn). Reviewed by Dr Alex J. Martin-Smith (LinkedIn). Published 25 July 2026, signatory lists last verified 25 July 2026. Both codes referenced here are voluntary and their signatory lists can change, so verify yours before relying on it. Speed figures in the charts are illustrative examples, not guarantees. This guide is information, not advice. Spotted something wrong? Tell us and we will publish the correction.