You really have not finished your question. We don't know if you mean
"Always the last three months from this date." Or do you mean the last
three months from the last of last month." Or do you mean you just
want to select any month, and have the query give you that month, plus
the two months before that month, or ?????
When you come up with what you want, generally, this example could be
expanded.
For the previous 3 months from today:
"Between DateAdd("m", -3, Date()) And Date()"
Put this into the criteria row of a query, in the date column you want
to select on, and you will get the last three months from today.