-51.22% is the change from 820 to 400
Calculation steps:
[( 400 - 820 ) ÷ 820] x 100 = -51.22%
Formula
Percentage change = [(400 - 820) / 820] x 100
Subtract the new number by the original number
400 - 820 = -420
-420 ÷ 820 = -0.5121951219512195
-0.5121951219512195 x 100 = -51.22%