-96.71% is the change from 639 to 21
Calculation steps:
[( 21 - 639 ) ÷ 639] x 100 = -96.71%
Formula
Percentage change = [(21 - 639) / 639] x 100
Subtract the new number by the original number
21 - 639 = -618
-618 ÷ 639 = -0.9671361502347418
-0.9671361502347418 x 100 = -96.71%