66.5% is the change from 600 to 999
Calculation steps:
[( 999 - 600 ) ÷ 600] x 100 = 66.5%
Formula
Percentage change = [(999 - 600) / 600] x 100
Subtract the new number by the original number
999 - 600 = 399
399 ÷ 600 = 0.665
0.665 x 100 = 66.5%
Example