Help with filter for Previous month's data.

[KEKeogh]

Okay, so I'm using the following formula to pull just the previous month's data:
_first_of_month(_add_months(current_date,-1)) and _add_days(_first_of_month(current_date),-1)

This seems to work fine on a general report pulling all data including the 1st and last of the previous month.

For some reason when I put this filter with a more detailed report.  The data for the last day of the Previous month doesn't show up.  Almost like it's looking for the last day of the previous month at midnight.

My fear is that one time a general report I create may no grab the last day's data.  Is there a way I can add a time constraint into the formula?

Thanks
Kathie