Queries :: Calculating Three Different Rolling Averages In One Query?

Is there a way to calculate three different rolling averages in one query?

I just inherited a database where someone is using three queries to capture the same information only with different time frames. They were calculating a rolling three month average, six month average, and twelve month average. I would like to combine these queries into one to reduce time spent running reports from the database. All three queries are based on one table. One of the columns in that table is called "Month Start Date". That field shows the first day of the month when a call was entered. I can get the query to tell me the first month in the three month period and the first month in the six month period, but I can't get it to calculate the averages of the calls that fall in those time frames. Here is the SQL for the query I have now. When I try to run this, I get the error message that my formula is not part of an aggregate function.

Code:
SELECT DISTINCT DateAdd('m','-2',(Max([Month Start Date]))) AS ThreeMonthStartDate, DateAdd('m','-5',(Max([Month Start Date]))) AS SixMonthStartDate, Max([Month Start Date]) AS MaxStartDate, IIf([Month Start Date] Between [ThreeMonthStartDate] And [MaxStartDate],Avg([All Call Rate]),' ') AS ThreeMonthAverageCallRate, LIST_WITH_TNC.Device, LIST_WITH_TNC.Model, LIST_WITH_TNC.[Item Num]
FROM LIST_WITH_TNC;

Is there a way to make this work?