SIM-only data guide
Best Data Rollover SIMs in the UK: Which Plans Let You Keep Unused Data?
For keeping unused UK data over several months, start with Sky Mobile Piggybank. Eligible fixed-data plans bank spare GB for up to 12 months. For a one-month safety net, iD Mobile and Asda Mobile Pay Monthly use last month’s saved data before the fresh allowance. O2, EE and Vodafone offer other forms of rollover on qualifying Pay Monthly or PAYG products, with different expiry and renewal rules.
The best rollover SIM is not necessarily the cheapest SIM — or even the one that carries the most gigabytes forward. The useful question is whether you will be able to spend that saved data before it expires, without paying more for the privilege than you save on top-ups or a larger allowance.
If you are ready to shop for a multi-month data bank, compare Sky Mobile SIM-only deals on DealPriceCheck. Its live View Deal cards provide the existing partner purchase route. Choose an eligible fixed-data plan, then compare the full minimum-term cost; a Sky Unlimited plan does not contribute or accept Piggybank top-ups.
Which data rollover SIM should you check first?
| What you want | Best place to start | Important limitation |
|---|---|---|
| Save data over several quiet months and withdraw it later | Sky Mobile Piggybank | Eligible data expires after 12 months; withdrawals are in whole GB and contract terms vary |
| Use last month's spare data automatically, before this month's data | iD Mobile Pay Monthly | Rollover lasts only one extra month; changing plans can clear it |
| Another Pay Monthly option with rollover used first | Asda Mobile Pay Monthly | One additional month; don't confuse it with Asda's PAYG bundles |
| Already on O2 or prefer its Plus/Ultimate benefits | Eligible O2 Pay Monthly | Current allowance is consumed before saved data; rolled data lasts one month |
| Want PAYG with data carried into the next qualifying plan | EE 30-day PAYG | Must renew an eligible plan within seven days; boosts and add-ons are excluded |
| Want Vodafone PAYG and automatic renewal | Eligible Vodafone PAYG Bundle | Total Rollover depends on automatic renewal, not irregular manual top-ups |
| Have an O2 Rolling Plan or Big Bundle | Eligible O2 PAYG product | Rolling Plans renew by card payment; Big Bundles rely on sufficient PAYG credit. Eligible core data is capped at one extra allowance |
| Rarely exceed your allowance | A smaller or cheaper SIM without confirmed rollover | Paying a premium to accumulate unwanted GB can be poor value |
These are distinct products, not a promise that every SIM from each network has rollover. In particular, a 30-day rolling contract is not the same thing as data rollover: the first describes commitment, while the second describes what happens to unused GB.
Sky Piggybank: best for saving data across several months
Sky Mobile's Piggybank differs from ordinary month-to-month rollover. Eligible unused data is moved into a separate account balance after a billing period; you can later use it to top up a compatible Sky SIM or, subject to the current rewards rules, exchange it for selected rewards.
Sky's published rules say unused data can remain in the Piggybank for up to 12 months. That makes it useful if your usage is seasonal rather than simply a little higher next month. Someone working mostly on Wi-Fi may save data for a later period spent travelling around the UK or tethering a laptop.
But there are real limits to that flexibility:
- Only eligible fixed-data Sky plans contribute spare data. An Unlimited Data plan does not generate Piggybank rollover.
- You need at least 1GB in the Piggybank and top-ups are made in whole gigabytes, not fractions.
- Eligible saved data can be shared across up to seven Sky SIMs on the same account, not with unrelated accounts. Piggybank top-ups cannot be added to a Sky Unlimited Data SIM.
- Each saved batch expires after 12 months if unused. Sky does not promise a fixed cash value per GB: rewards depend on the offers available when you redeem.
- A cheap-looking long-contract Sky SIM and a flexible 30-day Sky SIM are not equivalent purchases. Compare the minimum term, ongoing payments and any price changes before choosing.
Buying route: Compare Sky Mobile's current deals to find the allowance and contract you would genuinely use. For the detailed mechanics, read Sky's Piggybank explanation through our approved affiliate link. That second link is a help page, not a checkout; choose a suitable live plan through DealPriceCheck's View Deal route.
The Sky decision most people miss
If your usage stays at 5GB while you buy 25GB each month, Piggybank might grow rapidly — but you could be paying for more data than you will ever withdraw. On the other hand, if you use 5GB in winter but 30GB during repeated summer travel, the ability to bank data for longer has an obvious purpose. Compare your actual pattern, not the largest potential Piggybank balance.
iD versus Asda versus O2: three one-month rollovers that behave differently
These three options suit a different buyer from Sky: someone whose usage changes between adjacent billing periods, not someone trying to accumulate data for half a year.
iD Mobile: rolled data is used first
iD Mobile says unused eligible Pay Monthly data is added automatically to the next month's allowance. Rolled-over data is consumed before the new allowance, and anything still unused from the old month expires at the end of the following period. The ordinary new allowance can then create the next eligible rollover balance.
This order gives the saved data a good chance of being used. However, iD's guidance says changing plans resets rollover; a current balance should not be assumed to survive an upgrade or tariff change. Rollover is not useful on a genuinely unlimited UK data allowance because there is no fixed unused pot to carry.
Compare iD Mobile deals on DealPriceCheck if the network, term and underlying data price suit you. iD is not treated here as a confirmed DealPriceCheck affiliate partner.
Asda Mobile: another rollover-first Pay Monthly option
Asda Mobile is a genuine additional choice that should not be omitted from a UK rollover shortlist. Asda's official Pay Monthly product descriptions and contract terms say unused eligible inclusive data goes into the following month, is used before that month's new allowance and cannot be carried forward indefinitely.
This applies to the relevant Pay Monthly SIM contracts, not as a blanket claim about every Asda PAYG bundle. The contract term may be 12 or 24 months, so a useful rollover feature should not obscure the price and cost of leaving early. If you are considering Asda, view its current SIM-only offers and check the terms of the exact Pay Monthly plan.
O2 Plus and Ultimate: your new monthly data is used first
O2 also offers automatic rollover on eligible Plus and Ultimate Pay Monthly plans (for new and upgrading customers under its published terms), but its published order of use is reversed: the current month's main allowance is used before last month's rolled-over data. Any carried balance that remains unused after the next billing period expires; it does not keep accumulating.
O2 also restricts the source of rollover to the eligible main data allowance. Extra promotional data, some boosts and other special allowances do not necessarily qualify. O2's Pay Monthly rollover terms say rolled data is for UK use, not an extra free roaming balance. Unlimited plans are excluded.
That means an advertised 'double your data next month' outcome is possible under the scheme, but not guaranteed to be useful. A buyer whose normal month never exceeds the fresh allowance may never reach the older data at all.
What the same usage actually gives you
Assume an eligible 20GB allowance, 8GB used in month one, and 25GB used in month two. No purchased extras, promotional GB or separate roaming use are involved.
| Under those assumptions | iD / Asda rollover-first | O2 Plus/Ultimate main-data-first |
|---|---|---|
| Unused from month one | 12GB | 12GB |
| Available in month two | 32GB | 32GB |
| First 20GB of month-two use | Old 12GB + new 8GB | New 20GB |
| Final 5GB of month-two use | New 5GB | Old 5GB |
| Balance left at month-two end | 7GB of fresh allowance, potentially eligible to roll again | 7GB of old rolled data, which expires |
Both users had 32GB available in month two and made the same 25GB of use. Only the order of consumption changes what survives to month three. This is a worked illustration of the published rules, not a claim about a specific customer's bill or a guarantee that every Asda, iD or O2 product qualifies.
This is one reason a generic label such as data rollover included tells you too little to pick a SIM.
PAYG rollover: EE, Vodafone and O2 have renewal traps
Rollover on Pay As You Go can be useful without a long Pay Monthly commitment, but it is especially important to know what must happen at renewal.
EE: a seven-day renewal window
EE says its eligible 30-day PAYG plans carry unused main-plan data into the next qualifying plan. You can still receive rollover when there is a short gap, provided you start the next eligible plan within seven days of expiry. Rolled-over data lasts for that next plan period and is used before the new core allowance.
EE uses carried data before the new core allowance. Free Boosts and separately purchased add-ons do not roll over. If you miss the renewal window or move to an ineligible product, the old balance is lost. The same rules do not automatically apply to EE-network MVNOs such as Lyca or 1pMobile.
Vodafone: automatic renewal is the key
Vodafone's Total Rollover applies to qualifying Pay As You Go Bundles (also called Big Value Bundles) when the current bundle renews automatically. Eligible remaining allowances may then move into the next 30-day bundle. Irregular top-ups or a bundle that fails to renew do not produce the same outcome.
The word Total is a product name, not a promise of unlimited accumulation and not a standard Vodafone Pay Monthly benefit. Vodafone's published scheme includes eligible allowances beyond data, but this guide assesses its data value, not a second comparison of minutes and texts.
O2 Big Bundles and Rolling Plans: the payment method matters
O2 has separate PAYG rollover products from its Plus/Ultimate Pay Monthly scheme. Eligible Big Bundles renew from available PAYG credit: if the balance cannot pay for the next bundle on the renewal date, the saved data expires. O2's Rolling Plans instead renew automatically from a debit or credit card, provided payment succeeds.
The respective published schemes can carry up to 100% of the standard monthly data allowance into the next eligible period. A qualifying 10GB bundle can therefore provide at most 20GB for that next period, not an endlessly growing bank. Big Bundle terms also exclude promotional or bonus data and invalidate the saved balance if the customer changes tariff. Do not automatically apply O2's Pay Monthly fresh-data-first rule to these separate PAYG products without checking the precise product terms.
If PAYG is your priority, compare 30-day and no-contract alternatives for cost and network, then confirm the precise PAYG product independently. A 30-day SIM-only contract shown in the catalogue is not automatically a PAYG rollover bundle.
Does SMARTY give money back instead of rolling data over?
SMARTY's older Data Discount products reduced a later bill based on unused data; they were not a bank of GB that could be spent in a busy month. SMARTY now states that Data Discount plans are discontinued for new or switching customers. Existing subscribers may keep an old eligible plan if they do not change it. Do not buy a current SMARTY SIM expecting that historical discount or conventional rollover.
The money question: is paying more for rollover worthwhile?
You do not get cash back simply for carrying unused data forward. You have already paid for the allowance. Rollover is worth money only when you actually avoid a charge, a top-up, a higher-priced plan or an interruption that matters to you.
Consider two hypothetical SIM offers, on equally suitable networks and comparable terms:
| Illustrative offer | Allowance each period | Rollover | Cost per period |
|---|---|---|---|
| Plan A | 10GB | Yes, one month | £12 |
| Plan B | 20GB | No | £10 |
Suppose you use 6GB in the first period and 14GB in the second. Plan A carries 4GB into the second period and, if eligible, gives you exactly enough to use 14GB; you pay £24 over the two periods. Plan B covers both periods without rollover and costs £20. In that case the plan without rollover saves £4, even though 20GB expires unused in the first period.
These are illustrative prices, not a current real operator comparison. The point is to compare what you pay and actually consume. The result could reverse if the rollover plan were cheaper, if overage costs were high or if the banked data prevented a costly interruption.
Before buying, ask:
- When are your busy months? A one-month rollover helps a quiet month followed immediately by a busy one. Sky's longer Piggybank is more relevant when the peak is several months away.
- How much will you really use? If you repeatedly have 40GB unused, you may simply need a smaller plan. Start with our mobile data usage guide.
- What happens if you go over? Compare the real out-of-allowance or top-up rules, not an assumed universal cost per GB.
- What is the full commitment? A cheaper-looking 24-month plan can cost more to leave than a slightly dearer flexible plan. Check all scheduled payments and price rises.
- Does the network work where you use it? Saved GB cannot compensate for unusable indoor coverage. Our MVNO coverage and speeds guide covers why brands on one host network can still differ.
Sky rollover versus cheaper non-rollover deals: the buying decision
Sky is the main relevant affiliate shopping option here because it has a documented multi-month Piggybank. Compare current Sky Mobile deals and use the existing Awin-backed View Deal for the fixed-data plan whose total cost and contract suit you. This is the buying path; the Piggybank help link above only explains the feature and is not a checkout. The live provider page also contains Unlimited and differently priced/committed products, so do not assume all its cards provide the same rollover benefit.
Other plans can still be better buys. DealPriceCheck also lists Lebara, Lyca Mobile and 1pMobile. These are price, coverage and allowance alternatives, not verified rollover offers in the present comparison. If one costs less and already covers your busiest month, paying extra for Sky rollover may not make financial sense.
That distinction matters for network shopping as well. Sky uses O2's network, Lebara uses Vodafone infrastructure, and Lyca and 1pMobile are EE-based. A network relationship does not pass rollover, speed policies, eSIM features or roaming benefits from one retail brand to another. Do not infer rollover from a card's network badge.
What about the current deal cards on this guide?
The existing Current SIM-only alternatives to compare block is a live comparison of selected UK tariffs, not a list of certified rollover products. A card's GB amount, 5G badge or View Deal button does not prove a rollover entitlement. Compare price and network there; for a confirmed multi-month Piggybank route, use the relevant Sky provider page above. The existing card component, deal details and affiliate routing remain unchanged.
For anyone who frequently uses more data than a fixed plan provides, the better answer may be unlimited UK SIM deals, where there is no ordinary monthly fixed UK data bucket to carry. Rollover and unlimited solve different problems.