A 20GB to 40GB SIM only plan sits between a light allowance and unlimited. It suits regular mobile data use away from Wi-Fi, without paying for a cap you will not reach. The right deal in that band is not the one with the biggest number. It is the one that matches how you use your phone, on a network that works where you are, at a price that still looks reasonable after any mid-contract rise.
This guide explains how to choose. Live prices below are pulled from our database for allowances from 20GB to 40GB. We do not hardcode pounds-and-pence figures that go stale within days.
Cheapest 20GB to 40GB SIM only deals right now
Showing the lowest current monthly prices on available mobile deals with 20GB to 40GB of data. Confirm contract length, 5G, roaming and any price-rise terms on the specific plan before you buy.
Who a 20GB to 40GB plan is for
This range fits people who are past a small allowance but do not need unlimited. Typical use is social apps, maps, music and some video on mobile data, with Wi-Fi still covering a lot of the day. It is usually the wrong tier if your phone is on Wi-Fi almost all the time, or if you tether a laptop and stream for hours.
If you are consistently under about 10GB, start with our light data SIM guide. If you regularly use far more than 40GB, or your month-to-month use is unpredictable, the unlimited data deals guide is the better comparison. For how to judge "cheap" once you know the allowance, see how to find the cheapest SIM only deals.
How to choose a 20GB to 40GB deal
Work through these in order. A low monthly price only helps if the plan still works after you check coverage, term and what happens to the price later.
- →Price per GB. Divide the monthly price by the included data. Compare plans you would actually use. A cheaper 20GB plan can cost more per gigabyte than 30GB or 40GB, and a larger plan you will not finish is not better value.
- →Network coverage. Most lower-priced brands are MVNOs. They use EE, O2, Vodafone or Three masts, so coverage matches that host network. Check the host coverage map for home, work and the routes you travel. There is no separate signal for the SIM brand.
- →Mid-contract price rises. Many 12 and 24-month plans increase the monthly price during the term, often once a year. The rise can be a fixed amount or linked to inflation, and it differs by plan. Where our feed includes a rise, it is on the deal card. Compare the later price, not only the first month.
- →Contract length. A 30-day rolling plan lets you leave or switch with about a month's notice, which matters when prices move. A 12-month SIM can be cheaper each month and locks you in for the year. A 24-month term is a longer commitment and more exposure if a price rise applies.
- →5G. It is not included on every plan, even on a network that has 5G. You also need 5G coverage where you use the phone, and a handset that supports it. Treat 5G as a plan term to confirm, not as a default.
- →Roaming. EU roaming is not standard on every UK SIM. Some plans include a data allowance abroad, some cap it, and some charge a daily fee or restrict roaming. Check the plan you are buying if you travel.
Coverage follows the host network
A SIM brand does not build its own masts. If a plan runs on Vodafone, O2, Three or EE, that is the coverage you get, including 4G and 5G where that host has rolled it out and your plan and handset allow it. Two brands on the same host will not differ in signal. They differ in price, contract length, roaming, support and extras.
For how that wholesale model works, see what an MVNO is. If you want a closer read on a budget Vodafone option, our Talkmobile review covers that positioning without quoting a price that will date.
Rolling plans and fixed terms
In the 20GB to 40GB band you will see both 30-day rolling SIMs and 12 or 24-month contracts. Rolling plans are the flexible option: you can move when a better deal appears, using a PAC code. Fixed terms can look cheaper month to month, and they are also where mid-contract price rises are more common, because you are committed for longer.
The practical switching steps are in our PAC code guide. Rolling SIMs are also the usual route if you want to avoid a credit check. That is covered in the no credit check SIM guide. You can browse rolling plans on the 30-day SIM comparison.
Compare live 20GB+ SIM deals
The comparison filter is 20GB and above. There is no separate 20–40GB ceiling in the filters, so larger and unlimited plans appear in the same list. Prices update as deals change.
Compare 20GB+ SIM deals →Frequently asked questions
Is 20GB enough for a typical month?
It is enough for many people who use Wi-Fi at home and at work, and mobile data for maps, music, social apps and some video. It is tight if you stream for long stretches away from Wi-Fi or use your phone as a hotspot. Check the last month or two of mobile data use in your phone settings, then add a little headroom, before you pick 20GB over 30GB or 40GB.
Is a 40GB plan better value than unlimited?
Often, if you do not actually use unlimited. Unlimited plans are priced for heavy use, so a 20–40GB plan is usually the cheaper fit when your usage sits in that band. If you regularly go well past 40GB, or your usage swings a lot from month to month, compare larger allowances and unlimited on the live deals rather than assuming the bigger label is better value.
How do I compare price per GB?
Divide the monthly price by the included gigabytes. A lower headline price on a smaller allowance can cost more per gigabyte than a slightly higher price on 30GB or 40GB. Only count data you will use: paying for 40GB when you use 8GB is not a saving. Use the live price on the deal, including any introductory period, not a figure from an old article.
Do 20–40GB SIM only plans include 5G and roaming?
Not automatically. 5G depends on the plan, whether the host network has 5G where you use the phone, and whether your handset supports it. EU roaming is included on some plans, capped on others, and a paid extra on others. Read the plan terms for 5G and roaming before you buy. Coverage itself follows the host network (EE, O2, Vodafone or Three), not a separate SIM brand signal.
Will the monthly price rise during the contract?
It can. Many fixed-term plans from the major networks increase the monthly price during the contract, often once a year. The rise may be a set amount or linked to inflation, and it is not the same on every plan. Rolling plans are easier to leave if the price changes. Where our live feed includes a mid-contract rise, it is shown on the deal card. Compare the price after any scheduled rise, not only month one.
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