-90.09% is the change from 999 to 99
Calculation steps:
[( 99 - 999 ) ÷ 999] x 100 = -90.09%
Formula
Percentage change = [(99 - 999) / 999] x 100
Subtract the new number by the original number
99 - 999 = -900
-900 ÷ 999 = -0.9009009009009009
-0.9009009009009009 x 100 = -90.09%