Data rollover promises to make your mobile data-buying dollar stretch even further, but it's worth understanding the benefits and limitations.
Which Australian mobile networks offer "data rollover", and is it actually useful?
Data rollover is treated slightly differently depending on your carrier, but at the time of writing, Optus, Virgin, Telstra and Vodafone all have rollover provisions that work slightly differently depending on which network you're actually using.
Data rollover itself is almost self-explanatory. Each month as part of your mobile plan, along with whatever calling and texting quota you're given, you get a data allowance to use. At the end of the month, the unused data allowance vanishes, replaced with the data allowance for the next month.
Data rollover gives you the ability to have unused portions of your data allowance from your monthly mobile spend roll over into the following month or months rather than expiring on the 30th day of your plan.
So in simple terms, if your plan comes with 500MB of data to use in a given month, and you use 300MB in one month, a carrier that supports data rollover would shift the "unused" 200MB into your available pool of data for the following month. That sounds very simple, but the way that the providers currently offer data rollover has significant implications for how you can use it.
What about credit rollover?
Along with data rollover, many mobile providers over credit rollover on their plans. You can read all about it in our guide to credit rollover.
Telstra offers data rollover on its PrePaid Extra plans as long as you recharge within your 28 day expiry period. You can store up to a maximum of 50GB, and it will last for as long as you keep recharging more than $30 each month. Other Telstra prepaid plans do allow you to rollover unused call credit, but not data at the time of writing, although some of its prepaid plans will allow you to use unused credit to buy additional data top-ups.
Optus currently offers data rollover on its prepaid "Prepaid Ultimate Plus" plans. Under its data rollover offer, any unused data from your base offering is rolled over to the next month as long as you recharge prior to the expiry date. Data continues to collect month by month up to a maximum of 10GB. Only your base data is subject to rollover, so if you buy an additional data pack during the month, it will not roll over when it expires even if you do recharge.
Virgin Mobile's rollover offer is quite different to parent company Optus. Where Optus offers rollover to prepaid customers, Virgin Mobile's offer is for postpaid customers on its contract plans and includes not only data but also calling and text allocations.
Where it also differs from Optus' offering is in the duration of rollover. Under an applicable Virgin Mobile contract, data rolls over from one month to the next, but no longer. It is only used if you have already gone through your existing allocation for that month. If you don't use up your rolled over allocation, it will expire at the end of the next billing cycle.
What that means in effect is that your monthly allowance on Virgin Mobile is realistically a two month allowance before it vanishes, unlike Optus' rollover schedule which allows for actual long-term banking of your data allowance.
Virgin Mobile's pre-paid mobile plans, meanwhile, work the same as other providers', with "Prepaid Plus" plans supporting a maximum rollover of 12GB and "Prepaid Simple" plans supporting a maximum of 5GB.
Vodafone does allow for credit rollover if you recharge with the same plan type for most of its prepaid plans each month, although the permutations are quite complex, which you can see on Vodafone's web site.
Credit rollover isn't data rollover, however, and Vodafone's offering in this area is comparatively weak. If you purchase a data add-on you can roll over any unused data in that add-on as long as you purchase the same add-on again before the expiry date. The older data allowance then gets the same expiry period as the new add-on, which means you could theoretically keep rolling over as long as you kept recharging for as long as you like.
Is it worth it?
Data rollover relies on you continuing to recharge on the same plan, but does not attract any kind of additional fee no matter which provider you are connected to. As such there's not too much of a specific downside, as long as you keep in mind any limitations in terms of usage, such as the various caps on recharge data or Virgin's single-month expiry on post-paid plans.
It is also worth keeping in mind that you can always add data packs to existing mobile accounts for an additional fee each month. Those inclusions carry their own expiry dates, but allow you to quickly add data if you work out you're running short in a given month, whereas data rollover really only kicks in once the month is over. If you haven't already stored it, you can't dip into future months or anything like that. Another option worth considering if you find yourself running out of data is to sign up with a carrier that offers data pooling.
As a concept, data rollover is also really only valuable for consumers with quite variable data usage patterns. If you come close to or go over your data allocation each month, then you're not likely to be banking that much data, even within Virgin Mobile's shorter rollover period, to use in subsequent months. Equally, though, if you rarely hit your data peak, it will accumulate, but then you're not using that much data regularly anyway.