-51.28% is the change from 821 to 400
Calculation steps:
[( 400 - 821 ) ÷ 821] x 100 = -51.28%
Formula
Percentage change = [(400 - 821) / 821] x 100
Subtract the new number by the original number
400 - 821 = -421
-421 ÷ 821 = -0.51278928136419
-0.51278928136419 x 100 = -51.28%