-21.21% is the change from 646 to 509
Calculation steps:
[( 509 - 646 ) ÷ 646] x 100 = -21.21%
Formula
Percentage change = [(509 - 646) / 646] x 100
Subtract the new number by the original number
509 - 646 = -137
-137 ÷ 646 = -0.21207430340557276
-0.21207430340557276 x 100 = -21.21%