-84.39% is the change from 820 to 128
Calculation steps:
[( 128 - 820 ) ÷ 820] x 100 = -84.39%
Formula
Percentage change = [(128 - 820) / 820] x 100
Subtract the new number by the original number
128 - 820 = -692
-692 ÷ 820 = -0.8439024390243902
-0.8439024390243902 x 100 = -84.39%