Not enough to say anything yet

Low — this is a starting point, not a finding. More information would change it.

Nothing has been entered that can be turned into an answer. Every tool here works from figures you supply, and none of them will guess on your behalf.

What to try, all free

Look up what you actually used
Both Android and iOS keep a running total of mobile data, and your network shows the last few months in its app. That record beats every estimate on this page — use this tool to sanity-check it, not to replace it.
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Worked out by mobile rules 1.0.0. Nothing you entered leaves your browser.

Four symptoms, five or six causes

No service, weak signal, slow data and dropped calls feel almost identical to the person holding the phone. The things behind them are nothing like each other: a building that blocks signal, a mast with too many people on it, a SIM that has worn out, a handset fault, an outage, or 5G doing more harm than good at the edge of its range.

Nothing on the phone screen separates those. What separates them is comparison, and this page is mostly about which comparisons are worth going and making.

The two questions that do most of the work

Does anyone else nearby on the same network have it? This is the only thing that distinguishes a network problem from a problem with your phone or your SIM. One person with no signal is one person with no signal, however much it feels like the network has failed.

Does a different SIM work in your phone?If another SIM works, the handset is fine and the SIM or the account is not — and networks replace a failed SIM for nothing. If another SIM has the same problem, it is the handset.

Either answer rules out roughly half the possibilities. Both are free, and both need somebody standing next to you, which is why this page asks rather than assumes.

Why an outage is never diagnosed from one phone

Because the cost of getting it wrong falls entirely on the reader. Told their network is down, somebody waits for a fix. If what has actually happened is that their SIM has failed or their phone has developed a fault, they wait for a fix that is not coming, possibly for days.

So this tool will not reach an outage without corroboration from a second person on the same network in the same place, and until it has that it names the handset and the location as likelier. That is not caution for its own sake — it is the more probable explanation as well as the safer one.

Signal bars and speed are different things

A full signal means your phone is hearing the mast clearly. It says nothing about how many other people are talking to that mast at the same time. Good signal with slow data is the ordinary signature of congestion, and it is worst at predictable times — commutes, lunchtime, and anywhere with a crowd in it.

If it is fast at 7am and slow at 6pm in the same spot, that is what it is, and there is no setting on the phone that fixes it.

Wi-Fi calling is usually the answer indoors

Signal that returns as soon as you step outside is the building rather than the area. Foil-backed insulation, thick stone and modern coated glass are all extremely effective at stopping mobile signal, which is why newer and better-insulated buildings are often worse than older ones.

Wi-Fi calling routes calls and texts over your broadband instead of the mast. It is supported by all the UK networks, it is a setting rather than a purchase, and it solves the problem outright rather than improving it.

If your broadband is itself unreliable, that is a different problem with a different page — start with the broadband speed test and diagnosis.

What this tool does not do

It measures nothing. It has no access to your phone, your SIM or your network, and every conclusion is drawn from what you report. It also does not recommend a signal booster: cellular repeaters are regulated in the UK, the legal ones are narrower than the market suggests, and the free answer solves most of the cases people buy them for.