50% is the change from 66 to 99
Calculation steps:
[( 99 - 66 ) ÷ 66] x 100 = 50%
Formula
Percentage change = [(99 - 66) / 66] x 100
Subtract the new number by the original number
99 - 66 = 33
33 ÷ 66 = 0.5
0.5 x 100 = 50%
Example