-50% is the change from 400 to 200
Calculation steps:
[( 200 - 400 ) ÷ 400] x 100 = -50%
Formula
Percentage change = [(200 - 400) / 400] x 100
Subtract the new number by the original number
200 - 400 = -200
-200 ÷ 400 = -0.5
-0.5 x 100 = -50%
Example