-98.19% is the change from 830 to 15
Calculation steps:
[( 15 - 830 ) ÷ 830] x 100 = -98.19%
Formula
Percentage change = [(15 - 830) / 830] x 100
Subtract the new number by the original number
15 - 830 = -815
-815 ÷ 830 = -0.9819277108433735
-0.9819277108433735 x 100 = -98.19%