99.4% is the change from 501 to 999
Calculation steps:
[( 999 - 501 ) ÷ 501] x 100 = 99.4%
Formula
Percentage change = [(999 - 501) / 501] x 100
Subtract the new number by the original number
999 - 501 = 498
498 ÷ 501 = 0.9940119760479041
0.9940119760479041 x 100 = 99.4%