For each day over the last 90 days, how many users were active for at least one of the previous 30 days?
Like the query on daily average users, this is a basic query in Interana: measuring user activity over a specific time range. This sort of query is often the starting point for more in-depth explorations of your data.
Building the query
Since you're measuring use activity over time, use a Time view for this query. Then select the time range (90 days ago to now), and Count Unique users as a measure (select the column that represents your actors).
Because you want to see how many users were, on any given day, active for the previous month, set the Time Window to 1 Month and the Resolution to 1 day.
You can hover over any point to see the count of users who, on any day, were active for the previous month (each data point represents 1 day):