Broadband Speeds Explained

Everything you need to know about broadband speeds and what the terms mean.

It can be difficult to know what advertised ‘up to’ speeds for broadband really mean in terms of the speeds you’ll actually be able to achieve once you’ve signed up to the service. This guide aims to explain the factors affecting broadband speed, help you understand what different quoted speeds mean and give you the information you need to choose a broadband service with confidence.

How broadband speeds work

Most fixed line broadband services enter your home using your telephone line. Different broadband technologies have different maximum connection speeds, such as 24Mb or 80Mb. If a service uses copper telephone cables, then the length of the cable travelled over before entering your home will determine how much your actual broadband speed drops from the maximum speed. The further the distance, in copper cable length, the bigger the slowdown.

For the slower purely-copper services, it’s the distance in cable length from your local telephone exchange to your home that determines the slowdown. For newer services advertised as ‘Fibre Broadband’, fibre optic cables take over for the link from the telephone exchange to the nearest street cabinet, but the final connection from the cabinet to your home still goes over a copper telephone line (this arrangement is known as ‘fibre to the cabinet’ or FTTC). As such, Fibre Broadband that enters your home through your telephone line will still have some slowdown from the maximum speed; how much depends on the cable length from the street cabinet to your home.

The exception to these rules are Virgin Media’s fibre services, which tend to use steel coaxial cable from the street cabinet and shorter distances from cabinets to homes to ensure that the advertised speeds are usually enjoyed by all customers. Expensive ‘ultrafast’ and ‘hyperfast’ fully fibre optic, ‘pure fibre’, ‘fibre optic to the premises’ or ‘fibre optic to the building’ also tend to achieve the full advertised speed with little to no slow down due to distance, but at present these are mainly marketed to businesses and a few select residential locations due to their high installation costs.

Peak time slowdowns

As well as permanent speed limits from copper line length, all broadband services tend to experience some temporary slowdown in the speeds that customers can achieve during peak times.

Due to the nature of typical working and sleeping hours, there are certain times of the day that are more likely to be busy, and others that are likely to be relatively quiet. Even if the provider has invested heavily in ensuring that everyone is able to achieve fast connections at the busiest times, this capacity will be available to more people at less busy off-peak times like during the night when the majority of customers are asleep.

When a service is uncongested at off-peak times, you’ll be more likely to experience the maximum speed your broadband connection can achieve, while at the busiest times you may see some degree of slowdown.

How much slowdown your service suffers at peak times depends on how heavily your provider has invested in network capacity. The most expensive providers that tend to be primarily focused on business and home office users are likely to have more capacity than budget providers that make savings by compromising on capacity to spread it across more customers.

In the consumer market, providers who’ve advertised themselves as ‘truly unlimited’ tend to have invested more in their network capacity to achieve this, although buzzwords can also be used as a marketing ploy by budget providers so also pay attention to factors like ‘up to’ speeds, speed estimates and reviews before signing up.

Another factor to consider is that if your broadband provider mostly handles business connections then their busiest peak period is likely to be during the working day, rather than the more typical evening hours of most consumer broadband.

What advertised ‘up to’ speeds mean

It used to be the case that most providers would simply advertise the maximum possible speed available from the broadband connection, that which could be achieved over the very shortest lines, or only theoretically under ‘laboratory conditions’. As such, deals would be advertised as ‘up to 20Mb’ (or even ‘up to 24Mb’) for phoneline broadband and ‘up to 40Mb’ or ‘up to 80Mb’ for fibre services when virtually no one would be able to achieve these speeds.

A provider that made money by spreading less capacity over more lines, and so giving slightly slower speeds than their competitors at peak times, would be able to advertise their service with the same (or even higher!) ‘up to’ speeds as a competitor whose peak time performance was better.

Since the 1st of April 2012 the Advertising Standards Authority (ASA) and the Committee of Advertising Practice (CAP) have enforced guidelines that require advertised up to speeds to be consistently available to at least 10% of the users of that service. With these rules in place ‘up to’ speeds have dropped to a range of ‘up to 13Mb’ to ‘up to 16Mb’ for phoneline broadband and ‘up to 38Mb’ or ‘up to 76Mb’ for most fibre services.

It's now possible to see which providers will experience more of a slowdown at peak times due to congestion or over-subscription, as their advertised ‘up to’ speed will be lower than that of other providers offering similar services.

Minimum speeds

So ‘up to’ speeds are what 10% of customers achieve, but some customers with the longest copper telephone line cable lengths will be achieving much less.

On a purely phoneline-based broadband service, the lowest speed lines will tend to achieve only 0.5Mb, which is a big difference from the up to 13Mb to 16Mb that the fastest 10% achieve.

On a fibre to the cabinet service there tend to be much fewer customers whose lines are the very longest distances as there are many street cabinets for each exchange and the cabinets tend to be closer to even the most distant homes. However there is still a minimum supported broadband speed for these services of 15Mb, which is another significant drop from the up to 76Mb of the fastest 10%.

You would certainly want to know if you were about to sign up for a service advertised with a high speed when your line could only support the very lowest speed.

Average or typical speeds

The majority of customers will receive a speed somewhere between the advertised maximum and the lowest supported speed. But how do you determine what a typical or average speed for those services might be?

Some broadband providers will publish typical speeds that represent the speed that an average user of their service achieves. This might be given as a range where the lowest speed would be during evening peak hours and the fastest end achievable in the middle of the night.

If you can't find this information on the provider's site, Ofcom also publish speed monitoring reports giving the average speeds that different technologies and providers achieved at different times of the day. They also record the average of the maximum speeds recorded in each 24 hour period. Ofcom’s figures are based on monitoring of a connection's broadband usage over a long period of time, rather than occasional speed testing using a dedicated test, so they give a more realistic view of speeds during real world usage, which also tends to be lower than figures produced by speed tests like's. Ofcom do also record the fastest speeds each user monitored achieved every day, allowing them to average these figures and report an average maximum speed for each provider.

Ofcom's most recent figures for late 2016 found that advertised as ‘up to 17Mb’ phoneline broadband services tended to achieve average speeds of 9.75Mb, with variations depending on the ISP or the time of day. ‘Up to 38Mb’ fibre services averaged around 32.7Mb, 'up to 52Mb' fibre services averaged 47.3Mb and ‘up to 76Mb’ fibre services averaged 59.6Mb. Virgin Media's different speed tier fibre services tended to achieve average speeds lower than their advertised ‘up to’ speed the faster the advertised speed was. For example, 'up to 50Mb' on Virgin Media averaged at 41.8Mb, whereas the 'up to 200Mb' averaged at 79.3Mb (NB, Virgin Media has since added an 'up to 300Mb' product tier).

Estimated speeds

Now you know that an advertised ‘up to’ speed means that at least 10% of the service's customers will be able to consistently achieve that speed and you’ve seen Ofcom's published average speeds for different broadband technologies, but that doesn't tell you whether your telephone line is close enough to the telephone exchange or street cabinet to actually be able to achieve those speeds.

This is where tools like the checker come in, allowing you to enter your postcode (and in the case of fibre services your BT line rental phone number) to receive an estimate of the likely speed that lines within your postcode area, or your particular telephone line if you entered your number, will be able to achieve.

  • The communications regulator Ofcom has also published a voluntary code of practice to followed by broadband suppliers, which most have signed up for. This requires that broadband providers should:
  • Provide you with an accurate estimate of the likely range of speeds you’ll achieve with your line before you commit to signing up to the service
  • Explain clearly the factors that affect speed, such as the limits of the technology used and the length of copper cable involved
  • Give you help and advice if your speed is a little slower than expected and there’s something that they or you can do to fix this
  • If your speed is a lot slower than the original estimate, offer you an alternative faster product (if one is available) or let you out of your contract without any penalties

Lower than estimated speeds

Should you find that you're getting a much slower speed than your provider estimated at time of sign up, the Ofcom voluntary code of practice requires them to work with you and provide advice to increase your speed.

If your speed cannot be improved, then they should give you the offer of switching to a faster service, should one be available, or give you the option of leaving your contract early and without penalties.

If your provider's technical support and customer service team can't resolve the issue or don't allow you to leave your contract and you feel that this has been decided unfairly, then you may wish to make use of the ombudsman / dispute resolution scheme. To initiate this process you must first have made a written complaint to your provider. There are more details of how to make use of this scheme in our guide to making complaints.

Slow broadband speed could also be due to factors in your home setup that are not the fault of your provider, so it's worth ruling these out before casting blame on them. We've provided a set of tips to help speed up your broadband that should help you to test if any of these factors are slowing you down.

If you've been let out of your contract or you’re already out of your minimum contract term, you may also be able to get a faster connection by switching to a different provider, especially one running a different type of broadband. Use our broadband checker to see if faster or cheaper broadband is available in your area.

Upload speeds

Most of the information above refers to download speeds - how quickly you can get information from the Internet to your devices - but it's important to consider uploading as well.

How upload speed works

Upload speed refers to the rate at which information can be transmitted from your devices to sites and servers on the Internet. This affects things like cloud backup/sync of files, sending photos to sharing services or videos to sites like YouTube or Facebook.

Uploading tends to be seen as less important than how quickly you can download or stream content from the Internet, but as more and more services move on to the cloud, and more of us share videos with our friends and family, or with the world, this is becoming increasingly important.

Broadband technologies have limited capacity that's split between downloading and uploading. As download speeds tend to be seen as most important for home users, and are what’s advertised to sell broadband by speed, home broadband is usually split to give far more of the share to download.

Different types of broadband

Upload speeds tend to be particularly low on entirely phoneline broadband services where an up to 16Mb download connection might achieve as little as 0.75Mb to 1.5Mb. In rural and remote areas that are still on the older up to 8Mb services, upload speeds can be as little as 0.25Mb. The consolation in the case of phoneline broadband is that the frequencies used for upload speed tend to be those closest to voice, so they don't tend to slow down with distance from the telephone exchange, so a service getting the slowest supported download speed will still likely be enjoying the full supported upload speed.

For part-fibre, part-phoneline FTTC services (BT Superfast Fibre, Plusnet Fibre and many others), there are different upload speeds available. The slower services advertised as up to 38Mb tend to have up to 2Mb upload speed, while the faster up to 76Mb may be sold with up to 2Mb uploads or may have a faster option of up to 19.5Mb upload speed.

Virgin Media's part-fibre part-cable services, while tending to have faster upload speed, tend to allow less capacity for upload. Most services currently only offer 5% of the download speed, with up to 60Mb broadband services having only 3Mb uploading. For the fastest services the share is even less; the announced up to 152Mb service has only up to 12Mb upload.

Ofcom’s testing of home broadband speeds found that Plusnet had the fastest fibre upload speed, clocking in at an average of 16.8Mb in real world use.

Speed estimates

Unfortunately most price comparison don't yet give estimates for upload speed. However, the Ofcom voluntary code of practice, requiring speed estimates at sign up and efforts to fix the speed or let you out of your contract if real use doesn’t match the estimate, also applies to upload speeds.