-91.8% is the change from 256 to 21
Calculation steps:
[( 21 - 256 ) ÷ 256] x 100 = -91.8%
Formula
Percentage change = [(21 - 256) / 256] x 100
Subtract the new number by the original number
21 - 256 = -235
-235 ÷ 256 = -0.91796875
-0.91796875 x 100 = -91.8%