Last6Months = CALCULATE(SUM(Sales[Amount]), DATESINPERIOD(DateTable[Date], MAX(DateTable[Date]), -6, MONTH))
Use DATESINPERIOD for the Previous 6 Months:
Previous6Months = CALCULATE(SUM(Sales[Amount]), DATESINPERIOD(DateTable[Date], MAX(DateTable[Date]) - 180, -6, MONTH))
Create a Bar Chart, adding both measures to the Values and a time dimension (e.g., Month) to the Axis.
Format the chart to visually differentiate the two periods and add any slicers for dynamic filtering.
This will give you a dynamic comparison between the two 6-month periods.