-50% is the change from 36 to 18
Calculation steps:
[( 18 - 36 ) ÷ 36] x 100 = -50%
Formula
Percentage change = [(18 - 36) / 36] x 100
Subtract the new number by the original number
18 - 36 = -18
-18 ÷ 36 = -0.5
-0.5 x 100 = -50%
Example