[AC Question]

If I don't completely close an app from the phone, is data still charging my account?

[hallux]

That may depend on the app. If the developer decided to allow the app to do background refreshes (the Gmail app for example), it's entirely possible it'll use data when it's not the active app.

If you have Marshmallow or Nougat, you can use data saver features (unless your phone manufacturer has decided to turn the feature off) to restrict background data on an app-by-app basis.

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