-90.01% is the change from 991 to 99
Calculation steps:
[( 99 - 991 ) ÷ 991] x 100 = -90.01%
Formula
Percentage change = [(99 - 991) / 991] x 100
Subtract the new number by the original number
99 - 991 = -892
-892 ÷ 991 = -0.900100908173562
-0.900100908173562 x 100 = -90.01%