-1% is the change from 100 to 99
Calculation steps:
[( 99 - 100 ) ÷ 100] x 100 = -1%
Formula
Percentage change = [(99 - 100) / 100] x 100
Subtract the new number by the original number
99 - 100 = -1
-1 ÷ 100 = -0.01
-0.01 x 100 = -1%
Example