-62.32% is the change from 820 to 309
Calculation steps:
[( 309 - 820 ) ÷ 820] x 100 = -62.32%
Formula
Percentage change = [(309 - 820) / 820] x 100
Subtract the new number by the original number
309 - 820 = -511
-511 ÷ 820 = -0.6231707317073171
-0.6231707317073171 x 100 = -62.32%