If I recall my training correctly, you can use either a calendar month or a statement cycle of at least 4 weeks. Whichever you choose, it should be consistent (for that class of accounts).
Do your statements drop in the middle of the month because they are a separate type of account or do you cycle to avoid large mailings or other reason? We used to cycle throughout the month, but finally chose to put all transaction accounts on an end-of-calendar month cycle.
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I hear and I forget. I see and I remember. I do and I understand.--Confucius