Return measure based on previous time period

[Anonymous]

Hello community.

I have created a formula that should return the measure based on previous date. The formula is as follows.

VAR PeriodEnd = FIRSTDATE(Dates[Date])-1
VAR PeriodStart =
    PeriodEnd -
    DATEDIFF (
        FIRSTDATE(Dates[Date]),
        LASTDATE(Dates[Date]),
        DAY
    )
VAR Result = 
    CALCULATE(
        [Dækningsgrad nuværende],
        DATESBETWEEN(
            Dates[Date],
            PeriodStart,PeriodEnd
        )
)        
RETURN
    Result

 In my mind that should return my measure [Dækningsgrad nuværende] based on my Dates table. -1 period. And if i change (-1) with (-2) that should return my measure minus two periods. However it is not working.

If i set my dates as the following. Last period show 99,02%, but if i change to last period which in this instance would be 01-01-2020 - 31-12-2020

In the above example my measure "Dækningsgrad lastperiod" in 2020 should have returned as "Dækningsgrad 2nd last period" in 2021. Whereas second last period should be 2019. 

Dækningsgrad 2nd last period = 
VAR PeriodEnd = FIRSTDATE(Dates[Date])-2
VAR PeriodStart =
    PeriodEnd -
    DATEDIFF (
        FIRSTDATE(Dates[Date]),
        LASTDATE(Dates[Date]),
        DAY
    )
VAR Result = 
    CALCULATE(
        [Dækningsgrad nuværende],
        DATESBETWEEN(
            Dates[Date],
            PeriodStart,PeriodEnd
        )
)        
RETURN
    Result

Can you see what could be wrong?
Thanks in advance.

[v-shex-msft]

Hi @Anonymous,

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Xiaoxin Sheng

[amitchandak · Accepted solution]

@Anonymous , refer if these can help

same period based on date range
Last Period =
var _max =maxx(allseleceted(date),date[date])
var _min =maxx(allseleceted(date),date[date])
var datediff1 = datediff(_min,_max,day)
var _maxX = _max-datediff1
var _minX = _min -datediff1
return
CALCULATE(SUM(Sales[Sales Amount]),filter(all(date,date[date]<=_maxX &&date[date]>=_minX)))

same period based on date range year behind
Last Period =
var _max =maxx(allseleceted(date),date[date])
var _min =maxx(allseleceted(date),date[date])
var datediff1 = datediff(_min,_max,day)
var _maxX = eomonth(_max,-12)+1
var _minX = eomonth(_min,-12)+1
return
CALCULATE(SUM(Sales[Sales Amount]),filter(all(date,date[date]<=_maxX &&date[date]>=_minX)))