What DAX will calculate amount for same month in last months report? - powerbi

Question

I am struggling to work out the correct DAX measure to sum amount for the same period (e.g. month) but from a previous report.
Full Year forecast reports are provided monthly with a Report Date of EOMONTH for the month provided. These contain Amounts for each month in the year (called Period End Date, also dated EOMONTH). These are imported to a "Forecasts" table.
The following sample table replicates data from 3 separate monthly forecast reports, but rows are limited only to Jan-Mar months for simplicity (note - I have created Amounts based on concatenated month numbers for Report Date & Period End Date, for ease of identifying correct amounts in expected results):
Report Date
Period End Date
Amount
31 Jan 22
31 Jan 22
11
31 Jan 22
28 Feb 22
12
31 Jan 22
31 Mar 22
13
28 Feb 22
31 Jan 22
21
28 Feb 22
28 Feb 22
22
28 Feb 22
31 Mar 22
23
31 Mar 22
31 Jan 22
31
31 Mar 22
28 Feb 22
32
31 Mar 22
31 Mar 22
33
There is a "Dates" table, relationship = Dates[Date] to Forecasts[Period End Date], 1 to many, single direction. The user selects a single Report Date via a slicer creating filter context, visuals categories use Forecasts[Period End Date] for row context.
I've tried various methods but so far am unsuccessful, I'm having a mind meld and am probably overthinking this and therefore not looking at best method. One DAX example is:
Prev Month Forecast =
VAR _SelRptDate = SELECTEDVALUE( 'Forecasts'[Report Date] )
VAR _PreRptDate = EOMONTH( _SelRptDate, -1)
VAR _Result =
CALCULATE(
SUM( 'Forecasts'[Amount] ),
FILTER( 'Forecasts', 'Forecasts'[Report Date] = _PreRptDate)
)
RETURN _Result
Ideally I'd like to use an appropriate time intelligence function if one works for this. Happy to create inactive relationships if needed (e.g. Dates[Date] to Forecasts[Period End Date]). Preferably a Measure, not calculated column.
The following examples demonstrate expected results based on Report Date selected by the user:
Report Date = 28 Feb 22
Period End Date
Amount
Amount in Previous Report Date for Same Period End Date
31 Jan 22
21
11
28 Feb 22
22
12
31 Mar 22
23
13
Report Date = 31 Mar 22
Period End Date
Amount
Amount in Previous Report Date for Same Period End Date
31 Jan 22
31
21
28 Feb 22
32
22
31 Mar 22
33
23
Really appreciate any help / direction.
Thanks