Average Orders per Month measures the number of orders from customers you've received on average. It can be used to estimate your order volume and is useful to predict upcoming months.
Since the number of orders can fluctuate from month-to-month and over a year's cycle, it is useful to use at least a year's order data. That will allow the averaging to smooth out any highs/lows.
Eric Davis
Get a complete view of your customer behavior
The cohort analysis in Repeat Customer Insights will automatically build cohorts for all of your customers. It has the ability to go back through your entire store history so you can get a complete view of your customer behavior.