-50.58% is the change from 520 to 257
Calculation steps:
[( 257 - 520 ) ÷ 520] x 100 = -50.58%
Formula
Percentage change = [(257 - 520) / 520] x 100
Subtract the new number by the original number
257 - 520 = -263
-263 ÷ 520 = -0.5057692307692307
-0.5057692307692307 x 100 = -50.58%