-21.91% is the change from 817 to 638
Calculation steps:
[( 638 - 817 ) ÷ 817] x 100 = -21.91%
Formula
Percentage change = [(638 - 817) / 817] x 100
Subtract the new number by the original number
638 - 817 = -179
-179 ÷ 817 = -0.21909424724602203
-0.21909424724602203 x 100 = -21.91%