-51.4% is the change from 821 to 399
Calculation steps:
[( 399 - 821 ) ÷ 821] x 100 = -51.4%
Formula
Percentage change = [(399 - 821) / 821] x 100
Subtract the new number by the original number
399 - 821 = -422
-422 ÷ 821 = -0.5140073081607796
-0.5140073081607796 x 100 = -51.4%