-17.5% is the change from 120 to 99
Calculation steps:
[( 99 - 120 ) ÷ 120] x 100 = -17.5%
Formula
Percentage change = [(99 - 120) / 120] x 100
Subtract the new number by the original number
99 - 120 = -21
-21 ÷ 120 = -0.175
-0.175 x 100 = -17.5%
Example