In this guide
- How we put this guide together
- Data rollover at a glance
- What is SIM-only data rollover?
- Is data rollover worth it?
- Networks that offer SIM-only data rollover
- Vodafone
- O2
- iD Mobile
- Sky Mobile
- Asda Mobile
- SMARTY
- Which networks do not offer data rollover?
- Which network should you choose?
- Need help finding a SIM-only deal?
- Editorial policy
Several UK mobile networks let you carry unused data into a future month, but the rules vary a great deal. Some roll data over for one month only, while others let a much larger balance build up over time, and a few networks described as offering rollover actually do something different, such as discounting your next bill for the data you did not use. We have checked the current rules across the main UK providers below, so you can see which networks roll data over, for how long, and on which plans.
Reviewed by: Phil Brown, founder of SIM Only Finder. Phil previously worked in UK mobile retail at Three UK, advising customers on SIM plans, contracts, and network choices. He has spent over a decade running consumer comparison platforms and reviews networks and SIM-only deals based on that hands-on industry background. About the author
Last reviewed: October 2026. Updated regularly to reflect current network rollover terms, plan types, and fair usage rules.
How we put this guide together
To put this guide together, we reviewed the data rollover terms of the main UK networks and MVNOs in September 2026, checking how each scheme works, how long unused data lasts, and which plans qualify against each network's own help pages and terms. Where a network describes a feature as rollover but operates it differently, we have said so rather than list it alongside the others.
Data rollover at a glance
The table below summarises which networks currently roll data over and the main condition on each. The detailed sections follow.
What is SIM-only data rollover?
Data rollover lets you carry data you do not use in one month into the next, so it is not lost the moment your billing cycle resets. If you receive 5GB a month but use only 2GB, a network with rollover lets you carry the spare 3GB forward. The detail varies: some networks roll data over for one month only, and it is lost if you do not use it in time, while others let unused data build up over a longer period. Rollover is found across plan types, including one-month rolling SIMs, fixed-term SIM-only contracts, and Pay As You Go bundles, so a rollover SIM is not automatically a contract-free or pay-as-you-go product. Many networks also cap how much you can carry, and rolled-over data usually cannot itself be rolled over a second time.
Is data rollover worth it?
It depends on how steady your usage is. If some months are much quieter than others, rollover means you do not pay for data you never touch, and it is most valuable on smaller allowances where a quiet month makes a real difference. If you use close to your full allowance every month, rollover is unlikely to change much, because there is little spare data to carry. If you are not sure where you sit, our guide to how much mobile data you need walks through working it out from your own usage.
Networks that offer SIM-only data rollover
These are the UK networks that currently roll unused data over, and exactly how each one works.
Vodafone
Vodafone offers data rollover on its Pay As You Go Big Value Bundles rather than on its Pay Monthly SIM-only plans. Unused data, along with unused minutes and texts, rolls into the next 30-day period, up to one month's worth, and is then lost. For it to work you must renew the bundle within the 30-day period, and renewing early can void the rollover. It does not apply to Vodafone Pay Monthly SIM-only plans.
O2
O2 offers data rollover on its Pay As You Go rolling plans and on its Pay Monthly Plus and Ultimate plans, but not on standard Classic plans or unlimited plans. On the rolling plans it is capped by plan size: the £10 rolling plan includes 10GB and lets you roll over up to 10GB, giving a maximum of 20GB the following month. On Plus and Ultimate plans, up to 100% of your unused main allowance rolls into the next billing cycle, so you can carry at most one extra month's worth. Rollover is automatic, lasts one billing cycle only, and your fresh allowance is used before the rolled-over data.
iD Mobile
iD Mobile includes data rollover on every plan, and was the first UK network to offer it. It is automatic, with nothing to switch on. Unused data rolls into the following month only: it does not build up over time, so any data carried forward should be used within that next month or it is lost. There is nothing to roll on unlimited plans, since there is no unused allowance.
Sky Mobile
Sky Mobile has the most generous scheme. Rather than expiring after a month, unused data rolls automatically into your Piggybank each month and is kept for up to 12 months, so a balance can build up over time. You can share Piggybank data across up to seven SIMs on the account, so unused data can be passed to family members, and you can also cash it in for money off phones, tablets and accessories through Piggybank Rewards.
Asda Mobile
Asda runs an established mobile network using Vodafone's coverage. Asda Mobile offers data rollover on its Pay Monthly SIM-only plans, but not on its Pay As You Go bundles, where any unused data expires when the plan or add-on ends. On a Pay Monthly plan, unused data from your allowance rolls into the following month, with no limit on the amount carried from a single month. It does not build up beyond that, though: rolled-over data is used before your new monthly allowance, and only the previous month's leftover can be carried, so you cannot stockpile an endless balance.
SMARTY
SMARTY does not roll data over in the usual sense, but its approach is worth knowing. On its non-unlimited plans, instead of carrying unused data into the next month, SMARTY gives you money off your next bill for the data you did not use. If you regularly finish the month with data to spare and would rather pay less than bank it, that suits some people better than traditional rollover.
Which networks do not offer data rollover?
Not every network offers rollover. These popular networks do not currently include it:
This is not necessarily a drawback, as these networks may suit people who use most of their allowance each month and would not benefit from carrying data forward.
Which network should you choose?
Rollover is one factor among several, so it is worth weighing it against coverage, price and the other features each network offers. It tends to matter most on smaller allowances, where a quiet month makes a real difference, and least on large or unlimited plans. If you want data to build up over time, Sky Mobile's Piggybank is the strongest option; if you simply want a safety net for the odd light month, the one-month schemes from iD Mobile or O2 do the job. Our guide to whether 10GB is enough covers who smaller allowances suit.
Need help finding a SIM-only deal?
A SIM-only deal gives you data, minutes and texts without a handset, and comes either as a one-month rolling plan you can leave at any time or as a fixed-term contract, depending on the network. If you would like help finding the right one, including deals with data rollover, you can compare the current range or get in touch.
Editorial policy
This guide is produced by SIM Only Finder to help readers compare data rollover across UK networks. Network terms, plan types and rollover rules are checked regularly and updated to reflect current offers. Always confirm current terms directly with the network before signing up.
Tell your friends.