In Billing & Usage page you are able to view the storage usage per subscription months.
Click on the Billing & Usage link, under My Account menu:
Click on Storage Usage tab, to view the storage usage graphic for a selected period of time:
1. Click here to view the Storage History.
2. Here you can see the period of time split into months. Click on the link and you will be redirected to Storage usage page.
3. Here you can see the bandwidth consumption for each month.