-50% is the change from 630 to 315
Calculation steps:
[( 315 - 630 ) ÷ 630] x 100 = -50%
Formula
Percentage change = [(315 - 630) / 630] x 100
Subtract the new number by the original number
315 - 630 = -315
-315 ÷ 630 = -0.5
-0.5 x 100 = -50%
Example