-50.59% is the change from 850 to 420
Calculation steps:
[( 420 - 850 ) ÷ 850] x 100 = -50.59%
Formula
Percentage change = [(420 - 850) / 850] x 100
Subtract the new number by the original number
420 - 850 = -430
-430 ÷ 850 = -0.5058823529411764
-0.5058823529411764 x 100 = -50.59%