A Wi-Fi + Cellular iPad doesn't track cellular usage, because service is typically only sold in time and bandwidth units. The Settings > Cellular Data > View Account screen shows details from the carrier, including the billing period, how much data is included, and the data consumed so far in that period.
Turn cellular data on only when you need it
There are times when you'd prefer not to have an active cellular connection or cellular data link on an iPhone or cellular iPad, notably when you're close to the maximum of your monthly service plan or traveling outside an area included in your data plan (out of the country or in certain remote areas, typically). You can change how the cellular radio interacts with a network in two ways:
To turn off data only, in Settings > Cellular Data (iPad) or Settings > Cellular (iPhone), set the Cellular Data switch to Off. This disables the data link only. On an iPad, that's the entire link to a mobile broadband network; for an iPhone, you can still place and receive voice calls and send and receive SMS/MMS text messages.
To shut off the entire cellular connection, set Airplane Mode to On in the upper left of the main Settings screen, or tap the Airplane Mode button in the Control Center. Airplane Mode turns off all radios, not just cellular. It also dramatically extends your battery life in most cases.
You can also control other cellular data parameters:
Setting Enable LTE to Off will eliminate use of 4G LTE networks and rely on slower 2G and 3G networks. This is useful when LTE networks near you are spotty and you're having trouble staying connected as your device swaps back and forth between 2G/3G and 4G LTE. This can also reduce battery consumption in some cases.
In some markets, the Enable LTE option may read Voice & Data, and let you pick 2G, 3G, or LTE as network options.
Data Roaming can ensure that you don't consume cell bytes while you're outside the home area for your carrier. In some cases, you might have limits; in others, you might be charged. For instance, Sprint and Verizon allow roaming across their networks in areas they don't serve, but limit use to no more than 300MB per month.
Limit your activities on the cell network
Unless you are connected with Wi-Fi, limit your Internet-related activities to those that don't use much data, such as checking email or viewing Web pages.
Various items in Settings let you limit whether cellular data can be used for an app or activity, including:
Use the options in Cellular Data (iPad) or Cellular (iPhone) to prevent excessive use of certain services from consuming a lot of your data allocation. You can turn on and off specific apps, and see their data consumption.
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