If you are using limited mobile data then its wise to set usage limit according to your data plan “to avoid any extra charges” you will also get alerts when your mobile data usage exceeds its limit, this tutorial will help you to keep track of your mobile data quota.
Step # 1 Go to Settings > Data Usage “Option”.
Step # 2 Limit mobile data usage by dragging the orange line up and down according to your need. “set it according to when your month start and end”
That’s it… 😀
(Please note that This feature is Only available in android ice cream sandwich and in above version’s)