Within the Contacts section of your account you can see your Contact Growth. To get to this under the Contacts section, just click Reports along the top.
In your Growth Report you will see the overall growth for the past 30 days, but you can change this to show the last 60 or 90 days, the month to date or the year to date! Depending on what features you are using to Grow your List, you will also see the Growth by Source report. This will show you numbers for each of the sources, as long as you are using the source. If you want to find out more information about a particular source, maybe Text to Join or Scan to Join, just click on that Source and you will be taken to where you can find more information and even get started with that particular source.
How are you using your Growth reports? Have you seen trends in your reporting?