SIM-only data guide
30-Day vs 12-Month Unlimited SIM: Which Is Better Value?
Choose a 12-month unlimited SIM if its full committed cost is lower by enough to justify staying with that network. Choose a 30-day rolling unlimited SIM if you might switch, move, need service temporarily or want to test the signal before committing. Neither term is automatically cheaper: a discounted first payment, the actual renewal dates and possible exit charges can reverse the headline comparison.
The decision is not just £ per month. It is how much you will pay while you need the service, how much freedom you retain and whether the network can deliver usable unlimited data. Some deals renew every 30 days; others bill by calendar month even when labelled “monthly”. And a 12-month minimum term is a different concept from either billing schedule.
Already ready to compare? Start with current unlimited SIM-only deals and flexible 30-day SIMs. Check the data field on any flexible result: a 30-day plan with 100GB or 200GB is not an unlimited alternative.
At a glance: which commitment actually suits you?
| Your situation | Start with | The reason that could change your mind |
|---|---|---|
| You expect to keep the same SIM for at least a year | 12-month unlimited | A cheap rolling offer elsewhere may still beat the full contract price |
| You may move house, change jobs or leave the UK | 30-day rolling | A genuine 12-month saving may justify the commitment if the network is proven |
| You have never used this host network where you live | 30-day rolling or another low-commitment trial | A cheaper long term is poor value with unreliable indoor coverage |
| You need temporary broadband or a work hotspot | 30-day unlimited | Check tethering/device rules and whether a dedicated broadband product is better |
| You know this network works and the contract discount is significant | Compare a 12-month term against the same provider's rolling plan | The “12-month” tariff may have a different charging schedule or feature set |
| You only occasionally need more than 100GB | Check a large fixed-data plan first | Unlimited on either term may be unnecessary |
The key test: if flexibility has a monetary value to you, a small contract discount is not always worth locking away your ability to leave. If you know you will stay, compare actual total payments rather than paying extra for flexibility you will never use.
A real UK example: Lebara's rolling and 12-month unlimited plans
Comparing two operators with different coverage and conditions can hide the effect of the contract itself. For a more useful starting point, compare two published Unlimited variants from the same provider.
On 22 October 2026, Lebara's official UK product pages showed the following:
| Published Lebara Unlimited variant | Advertised price at the review | Commitment | Relevant difference |
|---|---|---|---|
| Unlimited Data Monthly Plan | £25 / 30 days | Rolling, with auto-renewal controls | Unlimited UK data and 100 international minutes on the named product |
| Unlimited Data 12-Month Plan | £22.50, displayed with “/30 days” wording | 12-month minimum commitment | Unlimited UK data and 100 international minutes on the named product; advertised 10% discount |
The £2.50 headline discount is 10%, but contract length and billing interval are not the same thing. Lebara's official 12-month FAQ says payments are taken at the start of each month, and that the signed-up price is fixed for the full 12 months. DealPriceCheck's corresponding 12-month Unlimited live card displayed a £270 minimum contract cost on 22 October 2026 (£22.50 × 12). Those are stronger grounds for a twelve-payment minimum-term illustration than the product page's ambiguous “/30 days” label alone. Check the written contract summary, actual payment dates and any separate extras before treating £270 as your final payable total.
Here are three different figures that must not be confused:
| Calculation at the dated prices | Amount | What it measures |
|---|---|---|
| Lebara 12-month Unlimited, 12 advertised monthly charges | £270 | The listed minimum contract cost, before any separate payable extras |
| Lebara rolling Unlimited, 12 exact 30-day renewals | £300 | 360 days of prepaid rolling service, not an entire calendar year |
| Lebara rolling Unlimited, 13 exact 30-day renewals | £325 | Upfront payments required for uninterrupted service through 365 days from a day-one start; the last payment also buys service beyond that year |
Comparing £270 and £300 gives a £30 difference across twelve payments, but not identical service duration. Comparing £270 and £325 gives a £55 first-year cash-outlay difference under the stated starting and billing assumptions, not a pure £55 difference in the value of service consumed in that year. If you allocate the £25 rolling price evenly across 365 days, the implied service-use cost is about £304.17, but that is an analytical allocation, not an invoice or a refund entitlement. Exact billing dates and the contract summary govern a real purchase.
Leaving early is the other material difference. Lebara's 12-month FAQ says cancellation before the term ends may require payment of the remaining balance; its terms describe an early-termination charge. A rolling-plan customer can generally stop future renewals using the account's auto-renewal control. This makes even a modest saving a commitment decision, not just an arithmetic comparison. Read the current written terms and request an account-specific exit quote if needed.
Buying route: Compare Lebara's 30-day and 12-month Unlimited offers on DealPriceCheck, inspect the named live card's Full plan details, then follow its existing Awin View Deal to the relevant checkout. There is no reason to send an Unlimited buyer to a generic international-calling page.
The figures above are a 22 October 2026 snapshot, not a permanent price promise. Do not substitute another Lebara Unlimited Plus or introductory offer just because it also says “Unlimited”.
What if a different provider is cheaper without a 12-month commitment?
A same-provider comparison shows the cost of commitment. It does not prove that provider is cheapest in the UK. For instance, 1pMobile offers a 30-day Unlimited Boost on EE's host network, while Lebara operates on Vodafone's network. Those aren't equivalent in coverage simply because both say Unlimited.
Compare 1pMobile SIMs on DealPriceCheck or view 1pMobile's products through our approved affiliate link. That link opens the operator's general product list, not a preselected Unlimited checkout. If another provider's suitable rolling plan costs less than your preferred 12-month deal, there is no financial reason to buy the longer term purely for its “discount”.
The overlooked billing problem: 30 days is not a calendar month
Twelve 30-day renewals cover only 360 days. A normal year has 365 days, so if you pay in advance for one consecutive 30-day bundle at a time and need uninterrupted service through day 365, the thirteenth bundle will normally begin on day 361.
That does not make every 30-day contract 13 payments per year: some “rolling monthly” products bill on calendar dates. Nor does it automatically make a 12-month minimum-term contract 12 bills: its billing interval must be checked separately.
Here is a strictly hypothetical prepaid 30-day example at £20 per renewal:
| What you calculate | Amount | What the figure actually means |
|---|---|---|
| 12 prepaid renewals | £240 | 360 days of service, five days short of a 365-day year |
| Cash paid to stay continuously covered for 365 days | £260 | 13th £20 renewal begins on day 361; service runs beyond day 365 |
| Service-value allocation for 365 days | About £243.33 | 365 × (£20 ÷ 30); an accounting comparison, not a payment or refund |
The thirteenth payment buys a new period, not an unexplained five-day fee. The unconsumed days may be useful next year; do not describe the whole last payment as wasted or assume unused prepaid service is refundable. A leap year, a partial refund, a billing-in-arrears plan or a provider-specific switching rule can change the picture. For Lebara's actual 12-month example, use the documented monthly minimum-term charge above; do not automatically impose this hypothetical 13-renewal model on it.
For an accurate comparison, record both cash paid by your target date and the value of any prepaid service extending past it. If the rival 12-month contract bills by calendar month, use its actual bill dates and charges, not the 30-day calculation above.
Calculate three different costs before choosing
Most cheap-looking unlimited deals only advertise one of the numbers you need. Write down all three:
- Minimum amount you are committed to pay. For a 12-month term, include its contractual price schedule, upfront fees and specified increases. For a rolling plan, the minimum obligation may be much shorter, but check its notice and cancellation rules.
- Cost for the time you genuinely need the service. Is that three months, eight months or at least a year? Count the appropriate calendar-month bills or 30-day renewals, introductory rates and later rates. Don't ignore another provider offering a cheaper suitable plan.
- Cost if you leave early. For a fixed term, ask about early termination charges. For rolling service, check any notice requirement, final billing and whether prepaid periods or credit are refunded.
These three totals answer different questions. A tariff can have the lowest full-year cost and still be the most expensive if your circumstances change after four months.
A cheap introductory bill is not the contract's average price
Suppose a hypothetical 12-month unlimited contract bills £12 for months 1–3 and £20 for months 4–12. With no other fees or increases, its first twelve bills cost (3 × £12) + (9 × £20) = £216, equivalent to £18 per calendar month across that term.
Its advert may emphasise “£12 a month”, but £12 does not describe the committed total. Likewise, an exact 30-day product advertising a discounted first three renewals must be calculated by renewals, not by assuming those three periods correspond to three calendar months.
If the agreed price schedule already includes a specified increase, don't add the same increase twice. Where an operator shows an effective monthly price or minimum contract cost in a comparison card, read how it was calculated, particularly on deals longer than twelve months.
Does a 12-month SIM protect you from price rises?
Not necessarily. A minimum term is a promise about how long the agreement lasts, not automatically a promise that every payment is identical.
Under Ofcom's rules for new contracts since January 2025, contractual price rises cannot be linked to inflation or expressed as percentages. If a provider includes a specified rise, it must set out the increase in pounds and pence and the date before you sign. Older contracts can have different terms. If a provider makes an unagreed detrimental change, separate exit rights may arise. See Ofcom's guidance on contract price rises.
Some operators offer no scheduled annual price rise on particular plans. Check the exact contract summary rather than assuming every 12-month plan rises each April or every 30-day plan remains the same price forever.
The price of being unable to change your mind
Imagine you choose a longer plan because it looks £2.50 cheaper per matched payment. Over four matched payments, that is only £10 of headline price difference, without adjusting for the differing billing intervals. If you discover that the network is poor in your new flat after four months, any remaining-term charge could outweigh the discount. £10 is illustrative arithmetic, not an actual saving over identical service dates or an early-exit fee. The fee depends on the agreement and the account's remaining commitment; for the Lebara 12-month example the provider expressly warns that the remaining balance may be payable.
On the other hand, if you have used that network at home and work for years and can comfortably stay for the minimum term, paying extra for a flexible tariff may offer no practical benefit.
Think of the difference as a flexibility premium. Ask yourself: What would it cost me to be on the wrong network, or need to switch, six months from now? A small discount can be a poor trade for a high exit risk; a substantial discount can be worthwhile when that risk is low.
A 30-day plan is flexible, but cancellation is not always instantaneous
A rolling contract may require notice or have a defined last billing date. Prepaid bundles can renew automatically unless stopped in time. You may receive no refund for a partly used period. “No long contract” does not necessarily mean that you can stop paying the same day you press cancel. For Lebara's specific 30-day rolling service, its help page explains how to turn off auto-renewal in the account to prevent a future renewal; this is not the same procedure as exiting its 12-month agreement.
For a fixed-term agreement, ask the provider for the actual early termination charge before initiating a switch. UK providers must supply key pre-contract information and a contract summary covering price, duration and termination conditions. For the wider rules, see Ofcom's checklist before taking out a contract.
A statutory distance-selling cooling-off right may apply to an eligible online purchase, but it has separate conditions and timescales; service already supplied may be chargeable. Do not mistake Lebara's offer to switch between qualifying 12-month products within the first 30 days for a general 30-day right to cancel a 12-month commitment without paying. Check the actual cancellation rights and charges for your purchase.
You can switch the number without cancelling it yourself
If you decide to move to another UK operator, you can normally retain your number. Text PAC to 65075, then give the code to the new provider. Use STAC to 75075 if you want to switch without retaining the number. To check contract status and potential charges without beginning the switch, text INFO to 85075.
A PAC is a transfer mechanism, not a waiver of your contractual balance. Don't manually cancel the old number first if you intend to port it. For the full steps and timing, see how to switch networks and keep your number, or Ofcom's mobile switching guidance.
Does “Unlimited” mean the same thing on both deals?
Before valuing the price difference, make sure you are buying comparable services. A 12-month bargain can lose to a flexible SIM if it has an unsuitable speed limit, weaker signal or less usable roaming data.
| Feature to compare | Why it changes the contract decision |
|---|---|
| Actual UK unlimited data | An unusually large 100GB or 200GB allowance is still a capped plan; don't mistake it for Unlimited |
| Network coverage at your address | A year of poor indoor reception is worse than a few pounds saved |
| Maximum speed / 5G access | Both plans may say 5G without identical performance or speed caps |
| Fair-use and traffic management | Unlimited does not always mean the same experience for very heavy usage |
| Hotspot and supported devices | A handset SIM is not necessarily permission to run an always-on household router |
| EU and other roaming | UK Unlimited does not automatically give unlimited overseas data; passes or separate caps may apply |
| eSIM and Wi-Fi Calling | Matters if your handset or local signal depends on these features |
| Minimum term and renewal rules | 12-month commitment and 30-day billing describe different things |
For example, 1pMobile's published unlimited policy says it may slow speeds at busy locations after more than 500GB in a Boost period. That is an operator-specific condition, not a universal 500GB cap and not proof that every Lebara, Lyca or other Unlimited deal behaves the same way. If your unlimited SIM will replace broadband, inspect the speed and tethering terms, not just the contract length.
Check the signal using Ofcom's coverage checker, remembering that predictions cannot guarantee reception inside your home. Our separate guide to hotspot and tethering SIMs covers the equipment and heavy-use questions; is unlimited mobile data really unlimited? covers fair-use rules in more detail.
Compare current unlimited SIM-only deals by term
Use the existing live Unlimited offer comparison on this page to shortlist genuinely unlimited UK-data tariffs. It already displays the provider, contract length and offer details. Review the current price schedule using Full plan details, then choose View Deal when the tariff suits you. These are existing DealPriceCheck routes; there is no need for a second catalogue or manually written imitation tariff cards.
Do not compare a 24-month plan's cheapest introductory payment with a 12-month plan's normal payment. A longer deal may appear among Unlimited offers, but it belongs in a separate full-term comparison. The relevant shortlist for this decision is a genuine rolling Unlimited tariff against a genuinely 12-month Unlimited tariff, followed by a check of suitable other networks.
For targeted discovery, use the Unlimited SIM-only catalogue and the flexible 30-day category. The second is not Unlimited-only: check that each offer really has Unlimited data before deciding.