-21.34% is the change from 820 to 645
Calculation steps:
[( 645 - 820 ) ÷ 820] x 100 = -21.34%
Formula
Percentage change = [(645 - 820) / 820] x 100
Subtract the new number by the original number
645 - 820 = -175
-175 ÷ 820 = -0.21341463414634146
-0.21341463414634146 x 100 = -21.34%