-50% is the change from 620 to 310
Calculation steps:
[( 310 - 620 ) ÷ 620] x 100 = -50%
Formula
Percentage change = [(310 - 620) / 620] x 100
Subtract the new number by the original number
310 - 620 = -310
-310 ÷ 620 = -0.5
-0.5 x 100 = -50%
Example