-51.06% is the change from 521 to 255
Calculation steps:
[( 255 - 521 ) ÷ 521] x 100 = -51.06%
Formula
Percentage change = [(255 - 521) / 521] x 100
Subtract the new number by the original number
255 - 521 = -266
-266 ÷ 521 = -0.510556621880998
-0.510556621880998 x 100 = -51.06%