-21.59% is the change from 820 to 643
Calculation steps:
[( 643 - 820 ) ÷ 820] x 100 = -21.59%
Formula
Percentage change = [(643 - 820) / 820] x 100
Subtract the new number by the original number
643 - 820 = -177
-177 ÷ 820 = -0.21585365853658536
-0.21585365853658536 x 100 = -21.59%