-21.32% is the change from 821 to 646
Calculation steps:
[( 646 - 821 ) ÷ 821] x 100 = -21.32%
Formula
Percentage change = [(646 - 821) / 821] x 100
Subtract the new number by the original number
646 - 821 = -175
-175 ÷ 821 = -0.21315468940316687
-0.21315468940316687 x 100 = -21.32%