-3.45% is the change from 521 to 503
Calculation steps:
[( 503 - 521 ) ÷ 521] x 100 = -3.45%
Formula
Percentage change = [(503 - 521) / 521] x 100
Subtract the new number by the original number
503 - 521 = -18
-18 ÷ 521 = -0.0345489443378119
-0.0345489443378119 x 100 = -3.45%