-2.5% is the change from 520 to 507
Calculation steps:
[( 507 - 520 ) ÷ 520] x 100 = -2.5%
Formula
Percentage change = [(507 - 520) / 520] x 100
Subtract the new number by the original number
507 - 520 = -13
-13 ÷ 520 = -0.025
-0.025 x 100 = -2.5%
Example