Why Your Broadband Speed Test Doesn’t Match the Advert
You signed up for a number. You run a speed test six months later and get a different, usually smaller, number. Before you assume something’s broken, it’s worth knowing that the advertised figure was never a promise in the first place. It was an average broadband speed.
That word is doing a lot of quiet work. Providers are allowed to advertise an average broadband speed rather than a guaranteed one, and the two are not the same thing.
What Does “Average Broadband Speed” Actually Mean on an Ad?
Under advertising rules set by the ASA, a provider can only call a figure the “average” speed if at least 50% of their customers actually achieve it during peak time, defined as 8pm to 10pm, when the most households are online at once. Roughly half of customers will be getting less than the advertised number even when the advert is perfectly accurate.
That’s a genuine tightening of the rules. Before 2018, providers only had to show an “up to” speed was achievable by 10% of customers, a much lower bar. The average speed rule is stricter, but it still isn’t a guarantee for any individual household.
The gap between the average broadband speed on the box and the number you actually get also depends heavily on the technology behind your line. Full fibre connections run at a consistent speed regardless of how far your house is from the local cabinet, so the average tends to sit close to what most households actually experience. Older copper based lines, including standard FTTC, lose speed the further the signal has to travel down the wire, which is why two neighbours on the same street and the same package can see genuinely different results.
The Rules Behind the Numbers (Checked August 2026)
| Term | What it actually means |
|---|---|
| “Average” speed | Achievable by at least 50% of customers at peak time (8pm-10pm) |
| Old “up to” speed rule | Only needed to be achievable by 10% of customers, phased out from 2018 |
| Minimum guaranteed speed | Given to you personally at point of sale, specific to your line |
| Right to exit | Applies if your speed drops below your minimum guaranteed speed and isn’t fixed within 30 days |
Figures checked against Ofcom’s Broadband Speeds Code of Practice and ASA advertising guidance, August 2026.
What’s a Minimum Guaranteed Speed, and What If You’re Below It?
This is the number that actually matters for your household, and it’s different from the average broadband speed used in adverts. Under Ofcom’s voluntary Code of Practice, participating providers must give you a personalised minimum guaranteed speed at the point of sale, based on your specific line, not a national average.
If your actual speed drops below that guaranteed minimum, your provider gets 30 days to sort it. If they can’t, you’re entitled to walk away penalty free, even mid contract. Our guide on your right to leave over slow broadband covers that process step by step, including how to log the fault properly so it counts. Ofcom’s own Broadband Speeds Code of Practice sets out which providers have signed up and what they’ve committed to.
How to Check What You’re Actually Getting
Key takeaways
- Find your minimum guaranteed speed on your original order confirmation or contract summary, not the advert you first saw.
- Test at peak time, 8pm to 10pm, since that’s when providers are legally judged too.
- Test with a cable into the router, then again over wifi, to see how much of any shortfall is your home network rather than the line itself.
- Log the date and result every time you test. A single bad reading proves little, a pattern over weeks proves a lot.
- Ask your provider directly for your minimum guaranteed speed figure if you can’t find it. They’re required to be able to give it to you.
None of this means the advertised average broadband speed is misleading by design. It’s a genuine average, measured and checked, and most providers publish theirs alongside the guaranteed minimum so you can see both figures side by side before you commit. The trick is simply knowing which number is the sales pitch and which one is the promise.
Our guide to what broadband speed you actually need is worth a look too, since a gap between the advertised average and your real number matters a lot more if you’re streaming and video calling at once than if you’re mostly browsing and emailing.
Worth ruling out first: a slow result at 8pm on a Sunday might just be everyone else on your street streaming at the same time, not a fault at all. Our evening broadband slowdown guide covers the difference between ordinary peak time congestion and a genuine fault worth reporting.
Frequently Asked Questions About Average Broadband Speed
A few extra questions worth clearing up once you know how the average broadband speed figure actually works.
- Is the average broadband speed the same as the minimum guaranteed speed?
- No. The average speed is a marketing figure roughly half of customers reach. Your minimum guaranteed speed is a personal number specific to your line, given at point of sale.
- Why is my broadband slower than the average speed advertised?
- Because “average” is designed to be met by around half of customers, not everyone. Line length, time of day and your own home network all affect your actual result.
- What time should I run a broadband speed test?
- Between 8pm and 10pm, since that’s the peak time window providers are measured against for advertising purposes.
- Can I leave my contract if my speed is below the average that was advertised?
- Not on the average figure alone. The right to exit applies when your speed falls below your own minimum guaranteed speed and isn’t fixed within 30 days.
- Do all broadband providers offer a minimum guaranteed speed?
- Most major providers sign up to Ofcom’s voluntary Code of Practice, but it’s worth checking your specific provider’s terms before you sign up.
