-19% is the change from 100 to 81
Calculation steps:
[( 81 - 100 ) ÷ 100] x 100 = -19%
Formula
Percentage change = [(81 - 100) / 100] x 100
Subtract the new number by the original number
81 - 100 = -19
-19 ÷ 100 = -0.19
-0.19 x 100 = -19%
Example