-4.71% is the change from 850 to 810
Calculation steps:
[( 810 - 850 ) ÷ 850] x 100 = -4.71%
Formula
Percentage change = [(810 - 850) / 850] x 100
Subtract the new number by the original number
810 - 850 = -40
-40 ÷ 850 = -0.047058823529411764
-0.047058823529411764 x 100 = -4.71%