66.5% is the change from 400 to 666
Calculation steps:
[( 666 - 400 ) ÷ 400] x 100 = 66.5%
Formula
Percentage change = [(666 - 400) / 400] x 100
Subtract the new number by the original number
666 - 400 = 266
266 ÷ 400 = 0.665
0.665 x 100 = 66.5%
Example