Exclude most recent month

Hello,
I have a query called qryReadmits based on a table called tblReadmits that
has fields such as ReadmitMonth, AccountNumber, Readmit (1 or 0), Population
(always 1). Data is populated into tblReadmits on a periodic basis.
Sometimes the data is fairly current (2 months behind) and other times it is
up to four months behind. I want to create a query where I group by month
the readmission rate which is Readmit divided by Population. But I want to
always exclude the most receent month that is available. I want to automate
this since I will be reporting it each month. Can someone give me ideas on
how to always exclude the most recent month regardless of how old the data is?

Thanks,