How do I find out which app is using up large amounts of data

[AC Question]

I have never exceeded 1 Gb in a month until recently when I am using 400 Mb every night after mid might. I want to find out which app is starting up and using that data. Is there a way I can check what app it is.

 

[belodion]

Settings, Data Usage, where the users are listed. But it may be a system app doing backups etc.

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