-20% is the change from 1000 to 800
Calculation steps:
[( 800 - 1000 ) ÷ 1000] x 100 = -20%
Formula
Percentage change = [(800 - 1000) / 1000] x 100
Subtract the new number by the original number
800 - 1000 = -200
-200 ÷ 1000 = -0.2
-0.2 x 100 = -20%
Example