To help us provide you with free impartial advice, we may earn a commission if you buy through links on our site. Learn more

“Guaranteed” broadband speeds explained

wifi router in a domestic setting with user in background

We explore why you might not be getting the speeds you’re paying for, ways to test your connection and how the best ISPs measure up

When ISPs (Internet Service Providers) advertise their broadband internet packages, the big “headline number” you see to represent the speed isn’t quite what it seems.

This number represents the maximum speed that the package can achieve, but this is more of an idealised goal than a realistic performance level you’ll get on a consistent basis. So, how fast is the connection you’ll actually get for your money? Before we get to the speeds that the best broadband providers guarantee, it’s useful to quickly explain the most important factors that make hitting that ideal speed difficult at times.

Factors that influence real-world speeds

There are a few reasons why the broadband connection supplying your home isn’t hitting the promised speeds you may be expecting. The number of potential reasons is practically endless (and could even include solar flares) but the list of most likely reasons is much shorter:

  • There’s network congestion as lots of people try to use the internet in your region at the same time. For example, when everyone’s watching 4K Netflix at dinner time.
  • You’re using Wi-Fi, which is subject to all sorts of interference and other bandwidth limits.
  • Your router simply can’t keep up with the bandwidth demands of all the devices in your home.
  • The server you’re connected to can’t provide data as fast as your connection can handle. For example a console game may only download at 300Mbits/sec when you might have much more than that available.

Some of these factors are beyond anyone’s control, some you’ll be able to have an impact on and others will solely be in the hands of the ISP. Your provider has to make sure everyone gets good usable service even during peak times, so they have to ration bandwidth occasionally.

many coloured wires plugged into mains broadband speed

That being said, with modern broadband, particularly fibre, you can expect speeds close to the maximum listed during quiet times, such as when downloading software overnight.

READ NEXT: Best mobile broadbands

What are “guaranteed” speeds?

A guaranteed speed is one which a service provider promises you’ll get as a minimum. If you experience speeds lower than this, they promise to rectify the issue within a certain time frame (usually 30 days) and this is the actual minimum speed you should expect. In other words, if you test your speeds and they’re between the guaranteed minimum and maximum, you’ve no grounds for complaining, because it’s within the service level in your contract.

Knowing what your guaranteed speed is rated as is both helpful when considering which provider to use, and to know when it’s time to lodge a complaint. If you’re already a subscriber, you can usually find mention of a guaranteed speed for your service in your contract, in accordance with Ofcoms’s voluntary code of practice for broadband speeds. Before you complain about slow internet however, it’s a good idea to first ensure that you’re testing your speeds correctly.

Test your speed the right way

The first thing you should know is the right way to test your broadband connection speeds. Some routers that come with an app will offer a speed test function, and this is the ideal way to test your connection because you’ll get a very accurate result.

If your router doesn’t have a built-in speed test, the next best way is by using an Ethernet cable directly connected to a device with a web browser or a speed testing app. In most cases this will be a laptop or desktop computer. You don’t want to use Wi-Fi as a variety of factors can affect its speed that have nothing to do with your actual line speed.

Finally, make sure your Ethernet cable, router and the device doing the speed testing are fast enough to handle your broadband speed. For example, if your router’s Ethernet ports are only rated for 100Mbits/sec then you’ll never see anything above that – even if you have Gigabit fibre.

Now that you know why you might not be getting the speeds you expect and how to test your speeds the correct way, let’s look at how some of the best broadband providers in the UK compare when it comes to their guaranteed speeds.

READ NEXT: Best broadband deals

Zen Internet

zen internet logo on a white background

Zen Internet was named our number one choice for a UK broadband provider in our Broadband Awards 2024, and it offers personalised guaranteed speeds. According to the company, customers will “get confirmation [of] your own minimum guaranteed speed when you join us.”

In addition to this, Zen Internet provides average download and upload speed claims “based on the download speeds of at least 50% of customers at peak time across the network.” Their “Fast” tier being 10Mbits/sec on average, their “Superfast” tier being 66Mbits/sec on average and their “Ultrafast” tier offering 900Mbits/sec on average. That is, according to Zen’s own data.

Zen Internet has also signed up to Ofcom’s voluntary auto compensation scheme, where their broadband users will receive automatic credit on their next bill if their service falls short of the minimum promised levels.

Read our full Zen Internet review


hyperoptic broadband logo on a white background

Hyperoptic’s minimum download speed guarantee applies to new customers who signed up from 17 June 2022. When you place an order with Hyperoptic, you’ll receive a contract summary that sets out the speeds you can expect, including the minimum speed.

Read our full Hyperoptic broadband review


three broadband logo on a white background

In its online documentation regarding network speeds, Three cites regulation (EU) 2015/2120 which lays out minimum speeds of 100Mbits/sec for 80% of a 24 hour period, when it comes to downloads on its Fixed Wireless Broadband Access. The minimum download speed for this service is 25Mbits/sec.

For 3G, 4G and 5G services, Three offers maximum download speeds of 2.5,10 and 25Mbits/sec respectively, but no global guaranteed minimum. Their online documentation does note that there’s a contractual minimum speed specified in the customer’s contract as part of the set of minimum, normal and maximum contractual speeds. The minimum speed is “achievable at least once in any 24 hour period in realistic usage conditions”.

Of course, these are reasonable terms considering the nature of mobile and wireless internet, which can be affected by many more factors than wired broadband such as fibre.

Read our full Three broadband review


plusnet logo on a white background

Like other providers that have become signatories to Ofcom’s Voluntary Speed Code of Practice, Plusnet will inform you of the minimum guaranteed speed for your connection as part of your contract documentation. Also, like other signatories, they will aim to rectify speeds below that guaranteed minimum within 30 days. If they can’t, you’ll be given the option to end your contract with them without an early termination charge.

Read our full Plusnet broadband review

Now Broadband

now broadband logo on a white background

Rounding out our comparison of minimum guaranteed broadband speeds is Now Broadband. Just like Plusnet and other Ofcom signatories to the Voluntary Speed Code of Practice, Now will inform you when you sign up what the minimum speed for your connection is.

They offer online technical checks so you can confirm that your line is in fact misbehaving, and if that proves to be the case and they can’t resolve the problem within 30 days, you’ll have the option of terminating your contract without an early termination fee.

Read our full Now Broadband review

Read more