99900% is the change from 1 to 1000
Calculation steps:
[( 1000 - 1 ) ÷ 1] x 100 = 99900%
Formula
Percentage change = [(1000 - 1) / 1] x 100
Subtract the new number by the original number
1000 - 1 = 999
999 ÷ 1 = 999
999 x 100 = 99900%
Example