-50.23% is the change from 645 to 321
Calculation steps:
[( 321 - 645 ) ÷ 645] x 100 = -50.23%
Formula
Percentage change = [(321 - 645) / 645] x 100
Subtract the new number by the original number
321 - 645 = -324
-324 ÷ 645 = -0.5023255813953489
-0.5023255813953489 x 100 = -50.23%