Having many apps on your Android phone can cost you a lot of data and there is a lot you can do to stop it, but one of the easiest places to start is to understand how each app you have installed uses data. Luckily, that information is very easy to find.
Go to Settings > Data Usage to find out how much data each of your apps are using. Scroll down and you will be able to see data usage at a glance. The list is automatically sorted in order of data use, so you’ll know straight away which apps are using the most data.
Tapping on any given app will offer up more details on how exactly that data is being used. You will find out how much of the data was used in the foreground (i.e. when you had the app open) and how much was used in the background.
You can restrict background data usage and change your apps auto-update setting to WiFi only to ensure that any auto-updates to that app occur only over WiFi.
There you can also get the info about the data usage month to month by tapping the date range at the top of the screen. You can then select from the previous months to see how your data usage, whether overall or for each app, has changed over the months.