Finding delta between certain dates while filtering the dates

Hi LFM 

Please try this:
First of all, I create a set of sample:

Then add a measure:

Diff = 
	VAR _currentDate = CALCULATE(
		MAX('Table'[Date]),
		ALLSELECTED('Table')
	)
	VAR _previousDate = CALCULATE(
		MIN('Table'[Date]),
		ALLSELECTED('Table')
	)
	RETURN
		CALCULATE(
			SUM('Table'[Values]),
			FILTER(
				ALLSELECTED('Table'),
				'Table'[Date] = _currentDate
			)
		) - CALCULATE(
			SUM('Table'[Values]),
			FILTER(
				ALLSELECTED('Table'),
				'Table'[Date] = _previousDate
			)
		)

The result is as follow:

Best Regards

Zhengdong Xu
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.