-2.56% is the change from 821 to 800
Calculation steps:
[( 800 - 821 ) ÷ 821] x 100 = -2.56%
Formula
Percentage change = [(800 - 821) / 821] x 100
Subtract the new number by the original number
800 - 821 = -21
-21 ÷ 821 = -0.025578562728380026
-0.025578562728380026 x 100 = -2.56%