All - Hours (Rolling) = CALCULATE(SUM('1 Combined - Frequency Data'[Hours Worked]), DATESINPERIOD ( '1 Combined - Frequency Data'[Month and Year], LASTDATE ( '1 Combined - Frequency Data'[Month and Year] ), -12, MONTH ) )
All - Hours (Rolling) = CALCULATE(SUM('1 Combined - Frequency Data'[Hours Worked]), DATESINPERIOD ( '1 Combined - Frequency Data'[Month and Year], LASTDATE ( '1 Combined - Frequency Data'[Month and Year] ), -12, MONTH ) )