On a typical prepaid plan, data you do not use disappears when the cycle ends. If you buy 10GB and use 4GB, the remaining 6GB is gone and next month starts at 10GB again. Two alternatives exist. Rollover carries some or all of the unused balance into the next cycle. Pay-as-you-go inverts the model entirely: you buy credit rather than an allowance, and you are only charged for what you consume. Both sound like savings, and both are worth less than they appear.
How the three models differ
| Standard allowance | Rollover | Pay-as-you-go | |
|---|---|---|---|
| You buy | A fixed monthly bucket | A fixed monthly bucket | Credit or a per-unit rate |
| Unused data | Expires at cycle end | Carries forward, usually with a cap or time limit | Never charged for |
| Overage | Throttled or you buy an add-on | Draws on the carried balance first | Charged at the per-unit rate |
| Best when | Your usage is steady | Your usage swings month to month | Your usage is very low or intermittent |
Why rollover rarely pays what it seems to
Rollover terms vary by carrier and are usually bounded in one of two ways: a cap on how much can accumulate, or an expiry on the carried balance after a cycle or two. Read which applies before you value the feature, because a bounded balance does not compound — you cannot bank six months of surplus and spend it on a long trip. What it reliably does is smooth one heavy month, which is insurance rather than a discount.
There is also a selection effect worth noticing. Rollover is most valuable to someone who consistently under-uses their plan. But someone who consistently under-uses their plan is, by definition, paying for a tier too large. The cheaper fix is to drop a tier, not to carry the waste forward.
Where pay-as-you-go genuinely wins
Pay-as-you-go is the right model for lines that barely run: a backup phone, a glovebox phone, a tablet used occasionally, a device for a child who is mostly on Wi-Fi. Because you are charged for consumption rather than availability, a line that uses almost nothing costs almost nothing.
It stops working as soon as usage becomes routine. Before choosing it, work out the per-gigabyte cost of the credit and compare it against the effective per-gigabyte cost of the smallest bucket plan you could buy instead. For most people the bucket wins once data is being used on most days, and the crossover arrives sooner than expected.
The question that actually saves money
Neither mechanism beats sizing the plan correctly. If you do not know what you use, the number is in your phone's settings under cellular or mobile data usage, and it is worth reading three consecutive months rather than one, because a single month with a holiday or a house move in it is not typical. Our data calculator turns that figure into a tier.
Once you have a real figure, the decision is usually simple. Steady usage means buy the tier just above your average and ignore rollover. Swinging usage means either buy for your peak or find a carrier that lets you change tiers freely mid-term, which several prepaid brands allow at no charge. Almost no usage means pay-as-you-go, and watch the dormancy window.
Jean Gilles has researched personal finance, consumer technology, and wireless pricing for over a decade. He founded ShopCellPlans in 2019 and writes every review on the site.
Frequently asked questions
Do unused gigabytes carry over on most prepaid plans? +
Does rollover data accumulate indefinitely? +
Is pay-as-you-go cheaper than a monthly plan? +
What is the best plan for a backup phone? +
How do I find out how much data I actually use? +
Should I pick a plan with rollover? +
One email when a carrier raises rates, drops a plan, or launches a deal worth switching for. No spam, unsubscribe anytime.
- Lycamobile plan terms and conditions, SIM and number expiry after 60 days of non-use — checked 3 September 2026
- Tello Mobile plan pages, Pay As You Go credit structure — as recorded in our verified plan data
