An unlimited data SIM removes the allowance altogether: no cap to watch and no charge for going over. It is the dearest tier each provider sells, so the useful question is not only which one is cheapest but whether you need it.
This page shows today's cheapest unlimited plans with the date they were read and the network each one runs on. It then sets out who unlimited suits, who should avoid it, and what the word does and does not promise. It also answers the question we used to cover on a separate page: are unlimited plans worth the money.
Who needs unlimited data, and who should avoid it
Unlimited suits you if you use your phone as a hotspot for a laptop or tablet on most working days. Video calls, software updates and cloud files on a computer use data far faster than the same person browsing on a phone.
It suits you if mobile data is your main internet connection at home, either because fixed broadband is poor where you live or because you move often and do not want a broadband contract.
It suits you if you stream video or music away from wifi for hours most days, and if you have already tried a large capped plan and hit the limit.
Avoid it if your phone is on wifi at home and at work. Most of your use never touches the mobile allowance, and a mid-sized plan will cover the rest for less.
Avoid it if you are buying it only for reassurance and have never checked what you use. Look first. Your phone's mobile data settings, or your provider's app, show the figure for recent months.
Avoid it, on any network, if that network is weak at your address. Unlimited does not make a poor signal faster.
Unlimited or a large capped plan: how to decide
Use the table of plans by data need above. The last two rows give you the cheapest plan of at least 100GB and the cheapest unlimited plan. The difference between them is the monthly price of having no cap.
Then make the comparison on the right network. The cheapest unlimited plan in the country is no use if it runs on the one network that struggles in your street. Find your strong network with the scanner and compare the plans that run on it.
If your usage is high but steady, the large capped plan is usually the better buy. If it is high and unpredictable, or you share the connection with other devices, unlimited saves you from an unexpected top-up or a throttled last week of the month.
What unlimited does and does not promise
Unlimited data means you will not be cut off or charged extra for the amount you use in the UK. Three other things are decided by the plan's terms, and they vary enough that you should read them.
Speed. Some providers sell more than one unlimited plan, with a cheaper one held to a lower top speed and a dearer one that is not. A speed-limited plan is fine for browsing, music and standard video, and frustrating for large downloads. The plan name and the small print say which you are buying.
Sharing your connection. Some plans allow unlimited tethering, some cap the amount you can share with other devices, and some restrict it. If you intend to run a laptop or a home router from the SIM, this is the term that matters most.
Fair use. Plans are sold for personal use, and providers keep the right to act on use they consider excessive or commercial. Allowances abroad are nearly always capped even when UK data is not.
We do not read speed limits, tethering terms or roaming allowances into our price tables. The tables tell you who is cheapest. The provider's plan page tells you whether that plan does what you need.
Coverage matters more with unlimited, not less
Heavy use exposes a weak signal quickly. A plan that is fine for messages can be painful for a video call from the same room. Before you buy, check the indoor result for your postcode and for anywhere else you plan to work from.
Each provider in the table sells its host network's signal. If Three is weak where you live, SMARTY will be weak there too, and the same holds for every other pairing in the Runs on column. Choose the network first and the brand second.
If the SIM is going to replace home broadband, test it in the room where the router or phone will sit, at the time of day you will use it most. Evening is when a busy mast slows down.
One-month plan or a longer contract
A one-month unlimited plan lets you find out how the network copes with your real use and leave if it does not. A 12 or 24 month contract may cost less each month but holds you to the term.
Our tables show the monthly price and not the contract length, so a low price can belong to either kind of plan. The provider's page states the term next to the price.
For contracts taken out since 17 January 2025, any price rise during the term has to be shown in pounds and pence when you sign up. Add it in when you compare a fixed contract with a one-month plan.
A sensible order is to run a one-month plan for a full month, use it as hard as you intend to, and only then decide whether a longer and cheaper contract on the same network is worth the commitment.
What our prices do and do not tell you
The table lists the providers whose unlimited plan we could read from their own website on the date shown. A provider that is missing may still sell one: it means we do not hold a dated price for it, not that it has none. The four networks' own plans are not in the table and can be opened from the links near the foot of this page.
If we cannot get fresh prices, the tables come off the page rather than show old ones. If a number here differs from the provider's site, the provider's site is right.