There is a widget on dashboard called "Recent Updated Lists", which shows the number of contacts added to the lists present in your account.

If you re not able to see this widget on the dashboard page, then click on "Edit Widgets" on the top and add it from there.

This widget can show the list additions made in your account for the past 30 days, and it also gives you an option to view these additions by selecting a specific Date/time range.