-97.12% is the change from 521 to 15
Calculation steps:
[( 15 - 521 ) ÷ 521] x 100 = -97.12%
Formula
Percentage change = [(15 - 521) / 521] x 100
Subtract the new number by the original number
15 - 521 = -506
-506 ÷ 521 = -0.9712092130518234
-0.9712092130518234 x 100 = -97.12%