-83.5% is the change from 600 to 99
Calculation steps:
[( 99 - 600 ) ÷ 600] x 100 = -83.5%
Formula
Percentage change = [(99 - 600) / 600] x 100
Subtract the new number by the original number
99 - 600 = -501
-501 ÷ 600 = -0.835
-0.835 x 100 = -83.5%
Example