Thanks for providing a PBIX
You didn’t specify how you wanted to deal with negative values, so I applied the same logic regardless of the sign. I’m sure you can adjust that to your needs, if you want to deal with that differently.
Percent Change Flipped =
VAR Perc = SUM ( 'Cost G3'[Total Contract Sum at G3] ) / SUM ( 'Cost G2'[Total Contract Sum at G2] ) -1
VAR Sign = IF( Perc <0 , -1, 1 )
VAR New = 1-ABS( Perc )
VAR Result = IF( Sign <0 , -New, New )
RETURN
Result
Here’s your sample file. Percent Change.pbix (30.6 KB)
I hope this is helpful.