-97.18% is the change from 639 to 18
Calculation steps:
[( 18 - 639 ) ÷ 639] x 100 = -97.18%
Formula
Percentage change = [(18 - 639) / 639] x 100
Subtract the new number by the original number
18 - 639 = -621
-621 ÷ 639 = -0.971830985915493
-0.971830985915493 x 100 = -97.18%