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Comparing T-Mobile and AT&T's rollover data plans

Both carriers have similar programs that allow customers to carry unused data from one month to the next, but it's not as simple as it sounds. This is how these rollover data plans really work.

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T-Mobile recently announced Data Stash, a program that allows customers to rollover their unused data each month. Shortly after, AT&T announced a similar program that also allows customers to carry unused data from one month to the next. Now the obvious question: Which plan is better?

Eligibility

T-Mobile's Data Stash program is available for Simple Choice plan customers with a smartphone plan that include 3GB or more of 4G LTE data. Tablet customers with plans of 1GB or more of 4G LTE data are also eligible. The Data Stash program isn't available for the $50 a month 1GB Simple Choice plan or T-Mobile's cheaper Simple Starter plans. It's also currently not available for prepaid customers, although the company has said that it may arrive in the future. Those customers that are eligible for Data Stash will also get 10GB of free data to start out. Rollover won't actually begin, however, until the entire 10GB is used.

AT&T's rollover program looks more appealing initially because there's no minimum amount of data required. You simply need to have an AT&T Mobile Share Value plan, which range from as little as 300MB a month all the way up to 100GB. That's covers about 50 million customers, according to an AT&T spokesperson.

Explaining rollover

Now let's break it down for both carriers. Say you have 5GB of data to use each month and in January you only use 2GB. Both T-Mobile and AT&T customers would add the remaining 3GB they didn't use in January to their normal 5GB plan, which would give them a total of 8GB of data to use in February.

Not too difficult, right? Well this is where the plans differ. As an AT&T subscriber, if you were to use only 4GB in February of the 8GB you stored up, only 1GB would roll over to March, which when added to your normal 5GB plan would give you a total of 6GB of data. This is because AT&T's rollover data expires after a single billing period. You would also expect the data that is being rolled over would be consumed first before any new data, but that's not the case. As noted on AT&T's website, "rollover data is always consumed last, after your other data allowances." Since the 3GB of data you carried over from January wasn't used in February, it simply disappears from your account, leaving you with only a single gigabyte of data to rollover to March.

Things are a bit simpler for T-Mobile subscribers because all of their unused data rolls over from one month to the next. Using the same example, if you were to use only 4GB in February of the 8GB you had in your Data Stash, the remaining 4GB of data would roll over to March for a total of 9GB of data to use. There is no limit to the amount of data that you can store, although data expires after 12 months. For instance, the 3GB of data I didn't use in January of 2015 will remain in my Data Stash until the same date in 2016 (unless I use it before then).

Family plans

The plans differ slightly when it comes to families. AT&T's rollover data is shared with all members of a family plan (up to 10 lines to be exact). If you have four lines in your family plan with 15GB of data and use only 10GB in a given month, 5GB of that data will rollover to the next month for a total of 20GB of data that is shared between all four lines. As is the case with individual plans, data will only rollover from month to month.

On T-Mobile, every line in a family plan that has a monthly allotment of at least 3GB of data will be eligible for Data Stash. The carrier will also give each eligible line in a family plan that same free 10GB offer. Unlike on AT&T, the stash is completely separate from other members of your family, but also won't expire for 12 months.

Conclusion

Both of these rollover plans are good for consumers. Personally, I favor T-Mobile. Despite the smaller coverage footprint, the 10GB of free data the carrier is handing out and the fact that the Data Stash won't expire for an entire year is more appealing to me. I also like that T-Mobile doesn't charge overages and instead will reduce your data speeds if you exceed your usage. Obviously, though, T-Mobile's network isn't for everyone. AT&T's rollover program can be seen as equally appealing because data can be shared across multiple devices and with family members.

Either way, rollover data is a win-win for consumers and a major step forward for the wireless industry.