-37.23% is the change from 830 to 521
Calculation steps:
[( 521 - 830 ) ÷ 830] x 100 = -37.23%
Formula
Percentage change = [(521 - 830) / 830] x 100
Subtract the new number by the original number
521 - 830 = -309
-309 ÷ 830 = -0.372289156626506
-0.372289156626506 x 100 = -37.23%