Why is my mobile data slow?
Full signal and slow data is not a contradiction. Signal strength and speed measure different things, and confusing them sends people looking in the wrong place.
Signal strength is not speed
The bars tell you how clearly your phone can hear the mast. They say nothing about how many other people are talking to that same mast at the same moment.
A mast has a finite amount of capacity and it is shared. Five bars in a railway station at 08:30 means you have an excellent connection to something that is extremely busy. This is the single most common cause of slow mobile data, and no setting on the phone changes it.
How to confirm it is congestion
Congestion has a fingerprint: it is time-dependent and location-dependent, and it is not affected by anything you do to the phone.
Try the same spot at a quiet hour. If it is fast at 7am and slow at 6pm in the same place with the same bars, that is congestion and the diagnosis is finished. Commutes, lunchtimes, town centres, event venues and anywhere with a crowd are where it shows up.
When 5G is the problem rather than the fix
The frequencies 5G uses to deliver its highest speeds carry less far than 4G and get through walls less well. At the edge of a 5G cell a phone can hold onto a weak 5G signal and end up slower than it would have been on 4G.
Both Android and iOS let you prefer 4G, and switching back is just as easy. If forcing 4G makes it faster, you have found it. See is 5G worth paying more for? for when this is likely.
Have you used your allowance?
Some networks slow you to a crawl rather than cutting you off or charging more. This is worth ruling out early because it looks exactly like a network problem and is completely unaffected by anything you do to the phone.
Check your allowance in the network’s app. Also check whether you have hit a fair-use cap on an unlimited plan, or the tethering limit, which is often lower than the main allowance and separately metered.
The comparisons worth making
Is anyone else nearby on the same network affected? This separates a network problem from a problem with your phone or SIM, and it is the only thing that does.
Does it follow you? A problem that happens everywhere is very unlikely to be coverage. One that happens in a single place almost certainly is.
Does another SIM work in your phone? If it does, the handset is fine and the SIM or the account is not.
Our mobile signal troubleshooter walks through these and tells you which is worth finding out next given what you already know.
Things worth trying, in order
Restart the phone. It re-registers with the network and fixes a surprising share of sudden problems. Do this before changing any settings, so you know what actually helped.
Check whether a data saver is on. Low Data Mode and Data Saver deliberately slow background activity and can make things feel sluggish. If you turned one on during a tight month and forgot, this is it.
Try a different app or site.One slow service is one slow service. It is common to conclude the connection is broken when a single app’s servers are having a bad day.
Resetting network settings is a genuine fix for a phone that will not connect properly, but it is not a first step: it erases every saved Wi-Fi password along with paired Bluetooth devices. Make sure you can get back onto your home and work Wi-Fi before you do it.
If it is your Wi-Fi rather than your mobile data
Worth checking which one you are actually on when it is slow. If the problem is at home and the phone is on Wi-Fi, this is the wrong page — start with the broadband speed test and diagnosis.