-90.24% is the change from 830 to 81
Calculation steps:
[( 81 - 830 ) ÷ 830] x 100 = -90.24%
Formula
Percentage change = [(81 - 830) / 830] x 100
Subtract the new number by the original number
81 - 830 = -749
-749 ÷ 830 = -0.9024096385542169
-0.9024096385542169 x 100 = -90.24%